#include <bits/stdc++.h>
using namespace std;
int n, k;
int a[100010];
long long int p[100010];
int m[100010];
int main() {
  cin >> n >> k;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    p[i] = p[i - 1] + a[i];
    m[i] = m[i - 1];
    if (a[i] > 0) m[i] += a[i];
  }
  long long int maxi = 0;
  for (int i = k; i <= n; i++) {
    long long int tren = m[n] - m[i];
    tren += m[i - k];
    long long int zbr = p[i] - p[i - k];
    tren = max(tren, tren + zbr);
    maxi = max(maxi, tren);
  }
  cout << maxi;
  return 0;
}
