#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll mod = 1e9 + 7;
const ll inf = (1 << 30) - 1;
const ll infll = (1LL << 61) - 1;
int N, K, s;
ll sum, ans, a;
int main() {
  cin >> N >> K;
  vector<ll> T, S;
  for (int i = 0; i < N; i++) {
    cin >> a;
    T.push_back(T.back() + a);
    S.push_back(S.back() + max(0LL, a));
  }
  for (int i = K; i <= N; i++) {
    ans = max((S[N] - S[i]) + S[i - K] + max(0LL, T[i] - T[i - K]), ans);
  }
  cout << ans << endl;
}
