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

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

q = sum(p[:K])
ans = q
for i in range(K, N):
    q = q + p[i] - p[i - K]
    ans = max(ans, q)
print((ans+K)/2)
