N, K = map(int,input().split())
p = list(map(int,input().split()))

li = [0] * N
for i in range(N): li[i] = sum(range(1, p[i]+1)) / p[i]

ans, total = sum(li[:K]), sum(li[:K])
if N != K:
  for i in range(1, N - K + 1):
    total = total - li[i-1] + li[i-1+K]
    ans = max(ans, total)
  print(ans)
else: 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 li = [0] * N li [0] * N [0] 0 N for i in range(N): li[i] = sum(range(1, p[i]+1)) / p[i] i range(N) range N ans, total = sum(li[:K]), sum(li[:K]) ans sum(li[:K]) sum li[:K] li :K K total sum(li[:K]) sum li[:K] li :K K if N != K:
  for i in range(1, N - K + 1):
    total = total - li[i-1] + li[i-1+K]
    ans = max(ans, total)
  print(ans)
else: print(ans) N != K N K for i in range(1, N - K + 1):
    total = total - li[i-1] + li[i-1+K]
    ans = max(ans, total)
   i range(1, N - K + 1) range 1 N - K + 1 N - K N K 1 total = total - li[i-1] + li[i-1+K] total total - li[i-1] + li[i-1+K] total - li[i-1] total li[i-1] li i-1 i 1 li[i-1+K] li i-1+K i-1 i 1 K ans = max(ans, total) ans max(ans, total) max ans total print(ans) print ans K = map(int,input().split()) map(int,input().split()) K N, K = map(int,input().split()) map(int,input().split()) N p = list(map(int,input().split())) list(map(int,input().split())) p total = total - li[i-1] + li[i-1+K] total - li[i-1] + li[i-1+K] total ans, total = sum(li[:K]), sum(li[:K]) sum(li[:K]) ans total = sum(li[:K]), sum(li[:K]) sum(li[:K]) total ans = max(ans, total) max(ans, total) ans li = [0] * N [0] * N li
N, K = map(int,input().split())
p = list(map(int,input().split()))

li = [0] * N
for i in range(N): li[i] = sum(range(1, p[i]+1)) / p[i]

ans, total = sum(li[:K]), sum(li[:K])
if N != K:
  for i in range(1, N - K + 1):
    total = total - li[i-1] + li[i-1+K]
    ans = max(ans, total)
  print(ans)
else: print(ans)