N,K = map(int,input().split())
A = list(map(int,input().split()))
wa = [0] * (N+1)
for i in range(N):
    wa[i+1] = wa[i] + (A[i]+1)/2
Max = 0
for i in range(N-K+1):
    Max = max(Max,wa[K+i]-wa[i])
print(Max) N,K = map(int,input().split()) N map(int,input().split()) map int input().split() ().split () input split K A = list(map(int,input().split())) A list(map(int,input().split())) list map(int,input().split()) map int input().split() ().split () input split wa = [0] * (N+1) wa [0] * (N+1) [0] 0 N+1 N 1 for i in range(N):
    wa[i+1] = wa[i] + (A[i]+1)/2 i range(N) range N wa[i+1] = wa[i] + (A[i]+1)/2 wa[i+1] wa i+1 i 1 wa[i] + (A[i]+1)/2 wa[i] wa i (A[i]+1)/2 A[i]+1 A[i] A i 1 2 Max = 0 Max 0 for i in range(N-K+1):
    Max = max(Max,wa[K+i]-wa[i]) i range(N-K+1) range N-K+1 N-K N K 1 Max = max(Max,wa[K+i]-wa[i]) Max max(Max,wa[K+i]-wa[i]) max Max wa[K+i]-wa[i] wa[K+i] wa K+i K i wa[i] wa i print(Max) print Max K = map(int,input().split()) map(int,input().split()) K wa = [0] * (N+1) [0] * (N+1) wa N,K = map(int,input().split()) map(int,input().split()) N Max = 0 0 Max A = list(map(int,input().split())) list(map(int,input().split())) A Max = max(Max,wa[K+i]-wa[i]) max(Max,wa[K+i]-wa[i]) Max
N,K = map(int,input().split())
A = list(map(int,input().split()))
wa = [0] * (N+1)
for i in range(N):
    wa[i+1] = wa[i] + (A[i]+1)/2
Max = 0
for i in range(N-K+1):
    Max = max(Max,wa[K+i]-wa[i])
print(Max)
