#include <bits/stdc++.h>

using namespace std;

ifstream fin ("deque.in");
ofstream fout ("deque.out");

int n, a[5000002], k;
deque<int>dq;

int main()
{
  fin >> n >> k;
  long long ans = 0;
  for (int i = 1; i <= n; i++) {
    fin >> a[i];
    while (!dq.empty() && dq.front() <= i - k)
      dq.pop_front();
    while (!dq.empty() && a[dq.back()] >= a[i])
      dq.pop_back();
    dq.push_back(i);
    if (i >= k)
      ans += a[dq.front()];
  }
  fout << ans;
  return 0;
}