n,k = map(int, input().split())
pn = list(map(int, input().split()))
qn = [(i+1)/2 for i in pn]
ans = sum(qn[:k])
t=ans
for i in range(1, n-k+1):
    t +=-qn[i-1]+qn[i+k-1]
    ans = max(ans, t)
print(ans) n,k = map(int, input().split()) n map(int, input().split()) map int input().split() ().split () input split k pn = list(map(int, input().split())) pn list(map(int, input().split())) list map(int, input().split()) map int input().split() ().split () input split (i+1)/2 for i in pn for i in pn i pn for i in pn (i+1)/2 i+1 i 1 2 qn = [(i+1)/2 for i in pn] qn [(i+1)/2 for i in pn] ans = sum(qn[:k]) ans sum(qn[:k]) sum qn[:k] qn :k k t=ans t ans for i in range(1, n-k+1):
    t +=-qn[i-1]+qn[i+k-1]
    ans = max(ans, t) i range(1, n-k+1) range 1 n-k+1 n-k n k 1 t +=-qn[i-1]+qn[i+k-1] t -qn[i-1]+qn[i+k-1] -qn[i-1] qn[i-1] qn i-1 i 1 qn[i+k-1] qn i+k-1 i+k i k 1 ans = max(ans, t) ans max(ans, t) max ans t print(ans) print ans t +=-qn[i-1]+qn[i+k-1] -qn[i-1]+qn[i+k-1] t ans = max(ans, t) max(ans, t) ans n,k = map(int, input().split()) map(int, input().split()) n pn = list(map(int, input().split())) list(map(int, input().split())) pn ans = sum(qn[:k]) sum(qn[:k]) ans k = map(int, input().split()) map(int, input().split()) k qn = [(i+1)/2 for i in pn] [(i+1)/2 for i in pn] qn t=ans ans t
n,k = map(int, input().split())
pn = list(map(int, input().split()))
qn = [(i+1)/2 for i in pn]
ans = sum(qn[:k])
t=ans
for i in range(1, n-k+1):
    t +=-qn[i-1]+qn[i+k-1]
    ans = max(ans, t)
print(ans)