N, K = map(int,input().split())
dices = list(map(int,input().split()))
list =[]
check=0
for i in range(K):
    check+=dices[i]
list.append(check)
for j in range(N-K):
    check -= dices[j]
    check += dices[j+K]
    list.append(check)    
print((max(list)+K)/2) N, K = map(int,input().split()) N map(int,input().split()) map int input().split() ().split () input split K dices = list(map(int,input().split())) dices list(map(int,input().split())) list map(int,input().split()) map int input().split() ().split () input split list =[] list [] check=0 check 0 for i in range(K):
    check+=dices[i] i range(K) range K check+=dices[i] check dices[i] dices i list.append(check) list.append list append check for j in range(N-K):
    check -= dices[j]
    check += dices[j+K]
    list.append(check)     j range(N-K) range N-K N K check -= dices[j] check dices[j] dices j check += dices[j+K] check dices[j+K] dices j+K j K list.append(check) list.append list append check print((max(list)+K)/2) print (max(list)+K)/2 max(list)+K max(list) max list K 2 K = map(int,input().split()) map(int,input().split()) K check=0 0 check check+=dices[i] dices[i] check check -= dices[j] dices[j] check list =[] [] list check += dices[j+K] dices[j+K] check dices = list(map(int,input().split())) list(map(int,input().split())) dices N, K = map(int,input().split()) map(int,input().split()) N
N, K = map(int,input().split())
dices = list(map(int,input().split()))
list =[]
check=0
for i in range(K):
    check+=dices[i]
list.append(check)
for j in range(N-K):
    check -= dices[j]
    check += dices[j+K]
    list.append(check)    
print((max(list)+K)/2)