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