N,K = map(int,input().split())
a = list(map(int,input().split()))
A = [0]*(N+1)
S = [0]*(N+1)

for i in range(N):
    A[i+1] = A[i]+max(0,a[i])
    S[i+1] = S[i]+a[i]

ans = -inf
for i in range(0,N-K+1):
    ans = max(ans,A[i]+max(0,S[i+K]-S[i])+(A[N]-A[i+K]))

print(ans)