from itertools import accumulate

n, k = map(int, input().split())
a = [0] + list(accumulate(map(int, input().split())))
print((max(a[i + k] - a[i] for i in range(n - k + 1)) + k) / 2) from itertools import accumulate n, k = map(int, input().split()) n map(int, input().split()) map int input().split() ().split () input split k a = [0] + list(accumulate(map(int, input().split()))) a [0] + list(accumulate(map(int, input().split()))) [0] 0 list(accumulate(map(int, input().split()))) list accumulate(map(int, input().split())) accumulate map(int, input().split()) map int input().split() ().split () input split print((max(a[i + k] - a[i] for i in range(n - k + 1)) + k) / 2) print (max(a[i + k] - a[i] for i in range(n - k + 1)) + k) / 2 max(a[i + k] - a[i] for i in range(n - k + 1)) + k max(a[i + k] - a[i] for i in range(n - k + 1)) max a[i + k] - a[i] a[i + k] a i + k i k a[i] a i k 2 n, k = map(int, input().split()) map(int, input().split()) n k = map(int, input().split()) map(int, input().split()) k a = [0] + list(accumulate(map(int, input().split()))) [0] + list(accumulate(map(int, input().split()))) a
from itertools import accumulate

n, k = map(int, input().split())
a = [0] + list(accumulate(map(int, input().split())))
print((max(a[i + k] - a[i] for i in range(n - k + 1)) + k) / 2)