#include <cstdio>
using namespace std;
int v[5000001],d[5000001],sfarsit,ln=1;
int main()
{ freopen("deque.in","r",stdin);
  freopen("deque.out","w",stdout);
  int n,k,i,sum=0;
  scanf("%d%d",&n,&k);
  for(i=1;i<=n;i++)
  { scanf("%d",&v[i]);
    if((i-k+1)>d[ln])
            ln++;
    while(v[i]<v[d[sfarsit]] && sfarsit>=ln)
            sfarsit--;
    d[sfarsit++]=i;
    if(i>=k)
    { sum=sum+v[d[ln]];
    }
  }
  printf("%d\n",sum);
    return 0;
}