N,K=map(int, input().split())
P=list(map(int, input().split()))
saikoro=[1+0.5*sai for sai in range(1000)]

ruiseki=0
for i in range(K):
	ruiseki+=saikoro[P[i]-1]

ans=ruiseki
for k in range(N-K):
	ruiseki=ruiseki-saikoro[P[k]-1]+saikoro[P[K+k]-1]
	ans=max(ans,ruiseki)
	
print(ans) 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 1+0.5*sai for sai in range(1000) for sai in range(1000) sai range(1000) range 1000 for sai in range(1000) 1+0.5*sai 1 0.5*sai 0.5 sai saikoro=[1+0.5*sai for sai in range(1000)] saikoro [1+0.5*sai for sai in range(1000)] ruiseki=0 ruiseki 0 for i in range(K):
	ruiseki+=saikoro[P[i]-1] i range(K) range K ruiseki+=saikoro[P[i]-1] ruiseki saikoro[P[i]-1] saikoro P[i]-1 P[i] P i 1 ans=ruiseki ans ruiseki for k in range(N-K):
	ruiseki=ruiseki-saikoro[P[k]-1]+saikoro[P[K+k]-1]
	ans=max(ans,ruiseki)
	 k range(N-K) range N-K N K ruiseki=ruiseki-saikoro[P[k]-1]+saikoro[P[K+k]-1] ruiseki ruiseki-saikoro[P[k]-1]+saikoro[P[K+k]-1] ruiseki-saikoro[P[k]-1] ruiseki saikoro[P[k]-1] saikoro P[k]-1 P[k] P k 1 saikoro[P[K+k]-1] saikoro P[K+k]-1 P[K+k] P K+k K k 1 ans=max(ans,ruiseki) ans max(ans,ruiseki) max ans ruiseki print(ans) print ans saikoro=[1+0.5*sai for sai in range(1000)] [1+0.5*sai for sai in range(1000)] saikoro ruiseki=0 0 ruiseki ruiseki+=saikoro[P[i]-1] saikoro[P[i]-1] ruiseki K=map(int, input().split()) map(int, input().split()) K P=list(map(int, input().split())) list(map(int, input().split())) P ans=ruiseki ruiseki ans ruiseki=ruiseki-saikoro[P[k]-1]+saikoro[P[K+k]-1] ruiseki-saikoro[P[k]-1]+saikoro[P[K+k]-1] ruiseki ans=max(ans,ruiseki) max(ans,ruiseki) ans N,K=map(int, input().split()) map(int, input().split()) N
N,K=map(int, input().split())
P=list(map(int, input().split()))
saikoro=[1+0.5*sai for sai in range(1000)]

ruiseki=0
for i in range(K):
	ruiseki+=saikoro[P[i]-1]

ans=ruiseki
for k in range(N-K):
	ruiseki=ruiseki-saikoro[P[k]-1]+saikoro[P[K+k]-1]
	ans=max(ans,ruiseki)
	
print(ans)