N,K = map(int,input().split())
p = list(map(int,input().split()))
math = [0]*N
ans = 0
check = 0
for i,j in enumerate(p):
    math[i] += (j*(j+1)/2)/j
    if(i+1<=K):
        check += math[i]
    else:
        check += math[i]
        check -= math[i-K]
    ans = max(ans,check)
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 math = [0]*N math [0]*N [0] 0 N ans = 0 ans 0 check = 0 check 0 for i,j in enumerate(p):
    math[i] += (j*(j+1)/2)/j
    if(i+1<=K):
        check += math[i]
    else:
        check += math[i]
        check -= math[i-K]
    ans = max(ans,check) i j enumerate(p) enumerate p math[i] += (j*(j+1)/2)/j math[i] math i (j*(j+1)/2)/j j*(j+1)/2 j*(j+1) j j+1 j 1 2 j if(i+1<=K):
        check += math[i]
    else:
        check += math[i]
        check -= math[i-K]
     i+1<=K i+1 i 1 K check += math[i] check math[i] math i check += math[i] check math[i] math i check -= math[i-K] check math[i-K] math i-K i K ans = max(ans,check) ans max(ans,check) max ans check print(ans) print ans p = list(map(int,input().split())) list(map(int,input().split())) p check -= math[i-K] math[i-K] check check += math[i] math[i] check check = 0 0 check math = [0]*N [0]*N math ans = 0 0 ans N,K = map(int,input().split()) map(int,input().split()) N K = map(int,input().split()) map(int,input().split()) K check += math[i] math[i] check ans = max(ans,check) max(ans,check) ans
N,K = map(int,input().split())
p = list(map(int,input().split()))
math = [0]*N
ans = 0
check = 0
for i,j in enumerate(p):
    math[i] += (j*(j+1)/2)/j
    if(i+1<=K):
        check += math[i]
    else:
        check += math[i]
        check -= math[i-K]
    ans = max(ans,check)
print(ans)