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