N,K=map(int,input().split())
P=list(map(lambda x: (int(x)+1)/2,input().split()))
s=tmp=sum(P[:K])
for i in range(K,N):
  tmp=tmp-P[i-K]+P[i]
  s=max(s,tmp)
print(s) 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)/2,input().split())) P list(map(lambda x: (int(x)+1)/2,input().split())) list map(lambda x: (int(x)+1)/2,input().split()) map lambda x: (int(x)+1)/2 (int(x)+1)/2 int(x)+1 int(x) int x 1 2 x input().split() ().split () input split s=tmp=sum(P[:K]) s sum(P[:K]) sum P[:K] P :K K =tmp=sum(P[:K]) tmp sum(P[:K]) for i in range(K,N):
  tmp=tmp-P[i-K]+P[i]
  s=max(s,tmp) i range(K,N) range K N tmp=tmp-P[i-K]+P[i] tmp tmp-P[i-K]+P[i] tmp-P[i-K] tmp P[i-K] P i-K i K P[i] P i s=max(s,tmp) s max(s,tmp) max s tmp print(s) print s N,K=map(int,input().split()) map(int,input().split()) N tmp=sum(P[:K]) sum(P[:K]) tmp s=max(s,tmp) max(s,tmp) s tmp=tmp-P[i-K]+P[i] tmp-P[i-K]+P[i] tmp s=tmp=sum(P[:K]) sum(P[:K]) s K=map(int,input().split()) map(int,input().split()) K P=list(map(lambda x: (int(x)+1)/2,input().split())) list(map(lambda x: (int(x)+1)/2,input().split())) P
N,K=map(int,input().split())
P=list(map(lambda x: (int(x)+1)/2,input().split()))
s=tmp=sum(P[:K])
for i in range(K,N):
  tmp=tmp-P[i-K]+P[i]
  s=max(s,tmp)
print(s)