#include <iostream>

using namespace std;

const int N(5e6);
int v[N], vmin(1e9);

int main()
{
  int n, k, smin(0);

  cin >> n >> k;

  for (int i = 0; i < n; i++)
  {
    cin >> v[i];
  }

  for (int i = 0; i < n - k + 1; i++)
  {
    //cout << v[i] << " ";
    vmin = 1e9;
    for (int j = i + 1; j < i + k; j++)
    {
      //cout << v[j] << " ";
      if (v[j] < vmin)
      {
        vmin = v[j];
      }
      if (v[i] < vmin)
      {
        vmin = v[i];
      }
    }
    //cout << vmin << " ";
    // cout << "\n";
    smin += vmin;
  }
  cout << smin;

  return 0;
}