#include <iostream>
#include <fstream>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int main()
{
    
    ifstream f("deque.in");
    int stg=0,dr= 0, n, k, array[5000001], deque[5000001];
    long int res = 0;
    f>>n>>k;

  for (int i = 1; i <= n; i++)
    f >> array[i];

  for (int i = 1; i <= n; i++)
  {
  
    while (stg <= dr && array[i] <= array[deque[dr]])
      dr--;
	  
    dr++;
    deque[dr] = i;

    if (deque[stg] == i - k)
      stg++;

    if (i >= k)
      res += array[deque[stg]];
	  
  }

  ofstream g("deque.out");
  g<<res;
  f.close();
  g.close();
  return 0;
}