N,K=map(int,input().split())
P=list(map(int,input().split()))
X=[]
for a in P:
    X.append(a/2+0.5)
gou=sum(X[0:K])

han=-32
saigou=sum(X[N-K:N])
han=saigou
for a in range(N-K-1):

    if gou>han:
        han=gou
    gou=gou-X[a]+X[a+K]

print(han) 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 X=[] X [] for a in P:
    X.append(a/2+0.5) a P X.append(a/2+0.5) X.append X append a/2+0.5 a/2 a 2 0.5 gou=sum(X[0:K]) gou sum(X[0:K]) sum X[0:K] X 0:K 0 K han=-32 han -32 saigou=sum(X[N-K:N]) saigou sum(X[N-K:N]) sum X[N-K:N] X N-K:N N-K N K N han=saigou han saigou for a in range(N-K-1):

    if gou>han:
        han=gou
    gou=gou-X[a]+X[a+K] a range(N-K-1) range N-K-1 N-K N K 1 if gou>han:
        han=gou
     gou>han gou han han=gou han gou gou=gou-X[a]+X[a+K] gou gou-X[a]+X[a+K] gou-X[a] gou X[a] X a X[a+K] X a+K a K print(han) print han P=list(map(int,input().split())) list(map(int,input().split())) P gou=sum(X[0:K]) sum(X[0:K]) gou N,K=map(int,input().split()) map(int,input().split()) N han=saigou saigou han X=[] [] X han=-32 -32 han K=map(int,input().split()) map(int,input().split()) K saigou=sum(X[N-K:N]) sum(X[N-K:N]) saigou han=gou gou han gou=gou-X[a]+X[a+K] gou-X[a]+X[a+K] gou
N,K=map(int,input().split())
P=list(map(int,input().split()))
X=[]
for a in P:
    X.append(a/2+0.5)
gou=sum(X[0:K])

han=-32
saigou=sum(X[N-K:N])
han=saigou
for a in range(N-K-1):

    if gou>han:
        han=gou
    gou=gou-X[a]+X[a+K]

print(han)