class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())


H,W=map(int,input().split())
S=[]
for i in range(H):
  S.append(list(input()))

rowGroups=UnionFind(H*W)
colGroups=UnionFind(H*W)

for i in range(H):
  for j in range(W):
    if j-1>=0 and S[i][j-1]=='.' and S[i][j]=='.':
      rowGroups.union(i*W+j,i*W+j-1)
    if i-1>=0 and S[i-1][j]=='.' and S[i][j]=='.':
      colGroups.union(i*W+j,(i-1)*W+j)
ans=0
for i in range(H):
  for j in range(W):
    ans=max(rowGroups.size(W*i+j)+colGroups.size(W*i+j)-1,ans)
print(ans) class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots()) UnionFind def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

     __init__ self.n = n self.n self n n self.parents = [-1] * n self.parents self parents [-1] * n [-1] -1 n self self n n def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

     find if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

     self.parents[x] < 0 self.parents[x] self.parents self parents x 0 return x x self.parents[x] = self.find(self.parents[x]) self.parents[x] self.parents self parents x self.find(self.parents[x]) self.find self find self.parents[x] self.parents self parents x return self.parents[x] self.parents[x] self.parents self parents x self self x x def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

     union x = self.find(x) x self.find(x) self.find self find x y = self.find(y) y self.find(y) self.find self find y if x == y:
            return

         x == y x y return if self.parents[x] > self.parents[y]:
            x, y = y, x

         self.parents[x] > self.parents[y] self.parents[x] self.parents self parents x self.parents[y] self.parents self parents y x, y = y, x x y y x self.parents[x] += self.parents[y] self.parents[x] self.parents self parents x self.parents[y] self.parents self parents y self.parents[y] = x self.parents[y] self.parents self parents y x self self x x y y def size(self, x):
        return -self.parents[self.find(x)]

     size return -self.parents[self.find(x)] -self.parents[self.find(x)] self.parents[self.find(x)] self.parents self parents self.find(x) self.find self find x self self x x def same(self, x, y):
        return self.find(x) == self.find(y)

     same return self.find(x) == self.find(y) self.find(x) == self.find(y) self.find(x) self.find self find x self.find(y) self.find self find y self self x x y y def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

     members root = self.find(x) root self.find(x) self.find self find x i for i in range(self.n) if self.find(i) == root for i in range(self.n) if self.find(i) == root i range(self.n) range self.n self n self.find(i) == root self.find(i) self.find self find i root if self.find(i) == root i return [i for i in range(self.n) if self.find(i) == root] [i for i in range(self.n) if self.find(i) == root] self self x x def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

     roots i for i, x in enumerate(self.parents) if x < 0 for i, x in enumerate(self.parents) if x < 0 i x enumerate(self.parents) enumerate self.parents self parents x < 0 x 0 if x < 0 i return [i for i, x in enumerate(self.parents) if x < 0] [i for i, x in enumerate(self.parents) if x < 0] self self def group_count(self):
        return len(self.roots())

     group_count return len(self.roots()) len(self.roots()) len self.roots() self.roots self roots self self def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

     all_group_members r: self.members(r) for r in self.roots() for r in self.roots() r self.roots() self.roots self roots for r in self.roots() r self.members(r) self.members self members r return {r: self.members(r) for r in self.roots()} {r: self.members(r) for r in self.roots()} self self def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots()) __str__ return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots()) '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots()) '\n'.join '\n' join '{}: {}'.format(r, self.members(r)) '{}: {}'.format '{}: {}' format r self.members(r) self.members self members r self self H,W=map(int,input().split()) H map(int,input().split()) map int input().split() ().split () input split W S=[] S [] for i in range(H):
  S.append(list(input())) i range(H) range H S.append(list(input())) S.append S append list(input()) list input() input rowGroups=UnionFind(H*W) rowGroups UnionFind(H*W) UnionFind H*W H W colGroups=UnionFind(H*W) colGroups UnionFind(H*W) UnionFind H*W H W for i in range(H):
  for j in range(W):
    if j-1>=0 and S[i][j-1]=='.' and S[i][j]=='.':
      rowGroups.union(i*W+j,i*W+j-1)
    if i-1>=0 and S[i-1][j]=='.' and S[i][j]=='.':
      colGroups.union(i*W+j,(i-1)*W+j) i range(H) range H for j in range(W):
    if j-1>=0 and S[i][j-1]=='.' and S[i][j]=='.':
      rowGroups.union(i*W+j,i*W+j-1)
    if i-1>=0 and S[i-1][j]=='.' and S[i][j]=='.':
      colGroups.union(i*W+j,(i-1)*W+j) j range(W) range W if j-1>=0 and S[i][j-1]=='.' and S[i][j]=='.':
      rowGroups.union(i*W+j,i*W+j-1)
     j-1>=0 and S[i][j-1]=='.' and S[i][j]=='.' j-1>=0 and S[i][j-1]=='.' j-1>=0 j-1 j 1 0 S[i][j-1]=='.' S[i][j-1] [i] S i j-1 j 1 '.' S[i][j]=='.' S[i][j] [i] S i j '.' rowGroups.union(i*W+j,i*W+j-1) rowGroups.union rowGroups union i*W+j i*W i W j i*W+j-1 i*W+j i*W i W j 1 if i-1>=0 and S[i-1][j]=='.' and S[i][j]=='.':
      colGroups.union(i*W+j,(i-1)*W+j) i-1>=0 and S[i-1][j]=='.' and S[i][j]=='.' i-1>=0 and S[i-1][j]=='.' i-1>=0 i-1 i 1 0 S[i-1][j]=='.' S[i-1][j] [i-1] S i-1 i 1 j '.' S[i][j]=='.' S[i][j] [i] S i j '.' colGroups.union(i*W+j,(i-1)*W+j) colGroups.union colGroups union i*W+j i*W i W j (i-1)*W+j (i-1)*W i-1 i 1 W j ans=0 ans 0 for i in range(H):
  for j in range(W):
    ans=max(rowGroups.size(W*i+j)+colGroups.size(W*i+j)-1,ans) i range(H) range H for j in range(W):
    ans=max(rowGroups.size(W*i+j)+colGroups.size(W*i+j)-1,ans) j range(W) range W ans=max(rowGroups.size(W*i+j)+colGroups.size(W*i+j)-1,ans) ans max(rowGroups.size(W*i+j)+colGroups.size(W*i+j)-1,ans) max rowGroups.size(W*i+j)+colGroups.size(W*i+j)-1 rowGroups.size(W*i+j)+colGroups.size(W*i+j) rowGroups.size(W*i+j) rowGroups.size rowGroups size W*i+j W*i W i j colGroups.size(W*i+j) colGroups.size colGroups size W*i+j W*i W i j 1 ans print(ans) print ans S=[] [] S class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots()) class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots()) UnionFind ans=0 0 ans H,W=map(int,input().split()) map(int,input().split()) H ans=max(rowGroups.size(W*i+j)+colGroups.size(W*i+j)-1,ans) max(rowGroups.size(W*i+j)+colGroups.size(W*i+j)-1,ans) ans W=map(int,input().split()) map(int,input().split()) W colGroups=UnionFind(H*W) UnionFind(H*W) colGroups rowGroups=UnionFind(H*W) UnionFind(H*W) rowGroups
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())


H,W=map(int,input().split())
S=[]
for i in range(H):
  S.append(list(input()))

rowGroups=UnionFind(H*W)
colGroups=UnionFind(H*W)

for i in range(H):
  for j in range(W):
    if j-1>=0 and S[i][j-1]=='.' and S[i][j]=='.':
      rowGroups.union(i*W+j,i*W+j-1)
    if i-1>=0 and S[i-1][j]=='.' and S[i][j]=='.':
      colGroups.union(i*W+j,(i-1)*W+j)
ans=0
for i in range(H):
  for j in range(W):
    ans=max(rowGroups.size(W*i+j)+colGroups.size(W*i+j)-1,ans)
print(ans)