n, k = map(int,input().split())
p = list(map(lambda x:int(x)+1,input().split()))

s = [0]*(n+1)

for i in range(n):
    s[i+1] = s[i] + p[i]
    
res = 0
for i in range(n-k+1):
    res = max(res,s[i+k]-s[i])
print(res/2) n, k = map(int,input().split()) n map(int,input().split()) map int input().split() ().split () input split k p = list(map(lambda x:int(x)+1,input().split())) p list(map(lambda x:int(x)+1,input().split())) list map(lambda x:int(x)+1,input().split()) map lambda x:int(x)+1 int(x)+1 int(x) int x 1 x input().split() ().split () input split s = [0]*(n+1) s [0]*(n+1) [0] 0 n+1 n 1 for i in range(n):
    s[i+1] = s[i] + p[i]
     i range(n) range n s[i+1] = s[i] + p[i] s[i+1] s i+1 i 1 s[i] + p[i] s[i] s i p[i] p i res = 0 res 0 for i in range(n-k+1):
    res = max(res,s[i+k]-s[i]) i range(n-k+1) range n-k+1 n-k n k 1 res = max(res,s[i+k]-s[i]) res max(res,s[i+k]-s[i]) max res s[i+k]-s[i] s[i+k] s i+k i k s[i] s i print(res/2) print res/2 res 2 p = list(map(lambda x:int(x)+1,input().split())) list(map(lambda x:int(x)+1,input().split())) p n, k = map(int,input().split()) map(int,input().split()) n k = map(int,input().split()) map(int,input().split()) k s = [0]*(n+1) [0]*(n+1) s res = max(res,s[i+k]-s[i]) max(res,s[i+k]-s[i]) res res = 0 0 res
n, k = map(int,input().split())
p = list(map(lambda x:int(x)+1,input().split()))

s = [0]*(n+1)

for i in range(n):
    s[i+1] = s[i] + p[i]
    
res = 0
for i in range(n-k+1):
    res = max(res,s[i+k]-s[i])
print(res/2)