N,K=map(int,input().split())
p=list(map(int,input().split()))
q=[]
q.append(0)
for i in range(len(p)):
  q.append(q[-1]+p[i])
maxi=q[K]-q[0]
for i in range(1,N-K+1):
  sub=q[K+i]-q[i]
  if sub>=maxi:
    maxi=sub
print((maxi+K)/2) 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 q=[] q [] q.append(0) q.append q append 0 for i in range(len(p)):
  q.append(q[-1]+p[i]) i range(len(p)) range len(p) len p q.append(q[-1]+p[i]) q.append q append q[-1]+p[i] q[-1] q -1 p[i] p i maxi=q[K]-q[0] maxi q[K]-q[0] q[K] q K q[0] q 0 for i in range(1,N-K+1):
  sub=q[K+i]-q[i]
  if sub>=maxi:
    maxi=sub i range(1,N-K+1) range 1 N-K+1 N-K N K 1 sub=q[K+i]-q[i] sub q[K+i]-q[i] q[K+i] q K+i K i q[i] q i if sub>=maxi:
    maxi=sub sub>=maxi sub maxi maxi=sub maxi sub print((maxi+K)/2) print (maxi+K)/2 maxi+K maxi K 2 maxi=sub sub maxi p=list(map(int,input().split())) list(map(int,input().split())) p maxi=q[K]-q[0] q[K]-q[0] maxi q=[] [] q sub=q[K+i]-q[i] q[K+i]-q[i] sub N,K=map(int,input().split()) map(int,input().split()) N K=map(int,input().split()) map(int,input().split()) K
N,K=map(int,input().split())
p=list(map(int,input().split()))
q=[]
q.append(0)
for i in range(len(p)):
  q.append(q[-1]+p[i])
maxi=q[K]-q[0]
for i in range(1,N-K+1):
  sub=q[K+i]-q[i]
  if sub>=maxi:
    maxi=sub
print((maxi+K)/2)