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