n,k=map(int,input().split())
p=[0]+list(map(int,input().split()))
for i in range(n+1):
  p[i]=(p[i]+1)/2
for i in range(n):
  p[i+1]+=p[i]
ans=0
for i in range(n-k+1):
  ans=max(ans,p[i+k]-p[i])
print(ans) n,k=map(int,input().split()) n map(int,input().split()) map int input().split() ().split () input split k p=[0]+list(map(int,input().split())) p [0]+list(map(int,input().split())) [0] 0 list(map(int,input().split())) list map(int,input().split()) map int input().split() ().split () input split for i in range(n+1):
  p[i]=(p[i]+1)/2 i range(n+1) range n+1 n 1 p[i]=(p[i]+1)/2 p[i] p i (p[i]+1)/2 p[i]+1 p[i] p i 1 2 for i in range(n):
  p[i+1]+=p[i] i range(n) range n p[i+1]+=p[i] p[i+1] p i+1 i 1 p[i] p i ans=0 ans 0 for i in range(n-k+1):
  ans=max(ans,p[i+k]-p[i]) i range(n-k+1) range n-k+1 n-k n k 1 ans=max(ans,p[i+k]-p[i]) ans max(ans,p[i+k]-p[i]) max ans p[i+k]-p[i] p[i+k] p i+k i k p[i] p i print(ans) print ans ans=0 0 ans n,k=map(int,input().split()) map(int,input().split()) n k=map(int,input().split()) map(int,input().split()) k p=[0]+list(map(int,input().split())) [0]+list(map(int,input().split())) p ans=max(ans,p[i+k]-p[i]) max(ans,p[i+k]-p[i]) ans
n,k=map(int,input().split())
p=[0]+list(map(int,input().split()))
for i in range(n+1):
  p[i]=(p[i]+1)/2
for i in range(n):
  p[i+1]+=p[i]
ans=0
for i in range(n-k+1):
  ans=max(ans,p[i+k]-p[i])
print(ans)