#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, K;
  cin >> N >> K;
  vector<int> a(N), sum(N + 1), good(N + 1);
  for (int i = 0; i < N; i++) {
    cin >> a[i];
    sum[i + 1] = sum[i] + a[i];
    good[i + 1] = good[i] + max(a[i], 0);
  }
  int res = 0;
  for (int i = 0; i <= N - K; i++) {
    res = max(res, good[N] - good[i + K] + good[i] - good[0]);
    res = max(res,
              good[N] - good[i + K] + good[i] - good[0] + sum[i + K] - sum[i]);
  }
  cout << res << endl;
  return 0;
}
