#include <bits/stdc++.h>
using namespace std;
bool vis[100005];
int n, k, a[100005];
long long ans;
int main() {
  scanf("%d%d", &n, &k);
  for (int i = 1; i <= n - k; ++i) {
    scanf("%d", &a[i]);
    if (a[i] > 0) ans += a[i], vis[i] = 1;
  }
  for (int i = n - k + 1; i <= n; ++i) scanf("%d", &a[i]);
  for (int i = n; i > k; --i) {
    if (a[i] > 0 && !vis[i]) {
      int sum = ans + a[i], sum2 = sum;
      for (int j = 1; j < k; ++j)
        sum -= a[i - j] * vis[i - j], sum2 += a[i - j] * (vis[i - j] ^ 1);
      if (sum > ans && sum > sum2) {
        for (int p = 1; p <= n; ++p) vis[i - p] = 0;
        ans = sum;
        vis[i] = 1;
      } else if (sum2 > ans && sum2 > sum) {
        for (int p = 1; p <= n; ++p) vis[i - p] = 1;
        ans = sum2;
        vis[i] = 1;
      }
    }
  }
  printf("%d", ans);
}
