#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {

    ll N,M;
    cin >> N >> M;
    vector<ll> A(N);
    vector<ll> sum(N+1,0);
    for(ll i = 0;i<N;i++){
        cin >> A.at(i);
        A.at(i) = max(A.at(i),0LL);
        sum.at(i+1) = sum.at(i) + A.at(i);
    }
    ll ans = 0;
    for(ll i = 0;i+M<N+1;i++){
        ans = max(ans,sum.at(i+M) - sum.at(i));
    }
    cout << ans << endl;

}