#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
  int v[5000010], i, n, k;
  long long sum;
  deque <int> q;

int main () {
  //int v[5000], i, n, k, sum = 0;
  fin>>n>>k;

  for (i = 1; i <= n; i++)
    fin>>v[i];

  for (i = 1; i <= n; i++) {

    while (!q.empty() && i >= 2 && v[i] <= v[q.back()])
      q.pop_back();
      
    q.push_back(i);
    if (q.front() <= i - k)
      q.pop_front();
    if (i >= k)
      sum += v[q.front()];
  }
  //sum += v[q.back()];
  fout<<sum;
}