#include <bits/stdc++.h>
using namespace std;
using namespace placeholders;
class sum_class {
  vector<int> v;

 public:
  sum_class(const vector<int>& vv) {
    v.resize(vv.size() + 1, 0);
    partial_sum(begin(vv), end(vv), begin(v) + 1);
  }
  int operator()(const int x, const int y) { return v[y + 1] - v[x]; }
};
int main() {
  int n, k;
  cin >> n >> k;
  vector<int> v(n);
  for (auto& x : v) cin >> x;
  vector<int> pv(n);
  transform(begin(v), end(v), begin(pv), [](const int x) { return max(x, 0); });
  sum_class sv(v), spv(pv);
  int rez = accumulate(begin(v), end(v), 0);
  for (int i = 0, j = k - 1; j < n; ++i, ++j) {
    rez = max(rez, spv(0, i - 1) + max(sv(i, j), 0) + spv(j + 1, n - 1));
  }
  cout << rez << endl;
  return 0;
}
