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