#include <iostream>
#include <fstream>
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");

int main()
{ int n, k;
  long long s = 0;
  fin >> n >> k;
  int a[n], deq[n];
  int frontt = 1, backk = 0;

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

  for (int i = 1; i <= n ; i ++)
  {
      while(frontt <= backk && a[i] <= a[deq[backk]])
        backk--;

      deq[++backk] = i;

      if( deq[frontt] == i-k)
        frontt++;

      if (i >= k)
        s += a[deq[frontt]];
  }

    fout << s;

    return 0;
}