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

cur = sum((X[i] + 1) / 2 for i in range(K))
ans = cur
for i in range(K, N):
    cur += (X[i] + 1) / 2 - (X[i - K] + 1) / 2
    ans = max(ans, cur)

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

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

cur = sum((X[i] + 1) / 2 for i in range(K))
ans = cur
for i in range(K, N):
    cur += (X[i] + 1) / 2 - (X[i - K] + 1) / 2
    ans = max(ans, cur)

print(ans)
