#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int a[N], n, k;
long long qian[N], quj[N], sum[N], ans;
int main() {
  scanf("%d %d", &n, &k);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    sum[i] = sum[i - 1] + a[i];
    qian[i] = qian[i - 1] + max(a[i], 0);
  }
  quj[n + 1] = 0;
  for (int i = n; i >= 1; i--) quj[i] = quj[i + 1] + max(a[i], 0);
  ans = 0;
  for (int i = 0; i <= n - k; i++)
    ans = max(ans, qian[i] + quj[i + k + 1] + max(sum[i + k] - sum[i], 0ll));
  printf("%lld\n", ans);
  return 0;
}
