#include<stdio.h>
#include<iostream.h>

#define NMAX 5000000

int n,k,i; long long suma;

int v[NMAX+5],deque[NMAX+5];

int main()
{
  freopen("deque.in","r",stdin);
  freopen("deque.out","w",stdout);

  scanf("%d %d",&n,&k);

  for(i=1; i<=n; i++) scanf("%d",v+i);

  int st=1,dr=0;

  for(i=1; i<=n; i++)
  {
    if(st<=dr && i-deque[st] == k) st++;

    while(st<=dr && v[i] <= v[ deque[dr] ]) dr--;

    deque[++dr]=i;

    if(i>=k) suma+=v[ deque[st] ];

  }

  printf("%lld\n",suma);


  return 0;

}