#include <stdio.h>


#define nmax 5000001
using namespace std;
int v[nmax], deque[nmax];
int back, front;
int main()
{ int n, k, i, sum=0;
    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]);
    back=0,front=1;
   for(i=1;i<=n;i++)
   {
       while(back>=front && v[i]<=v[deque[back]]) back--;
       deque[++back]=i;
       if(deque[front]==i-k)
       front++;
       if(i>=k) sum+=v[deque[front]];

   }
    printf("%d",sum);
    return 0;
}