#include <stdio.h>
#include <deque>
using namespace std;
deque <int> d;
int v[5000001];
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n, i, k, s = 0;
    scanf("%d%d",&n,&k);
    for(i=2;i<=n;i++)
    {
      scanf("%d",&v[i]);
      d.push_back(i);
      while(v[d.back()]<v[i] && !d.empty()){
        d.pop_back();
      }
      while(d.back()-d.front()+1 > k) {
        d.pop_front();
      }
      s += v[d.front()];
    }
    printf("%d",s);
    return 0;
}