#include <stdio.h>

int v[5000001],deque[5000001];
int n,k,i,dr,st=1;
long long s;

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]);
        while (v[i]<v[deque[dr]] && st<=dr) dr--;
        deque[++dr]=i;
        if (deque[st]==i-k) st++;
        if (i>=k) s=1LL*(s+v[deque[st]]);      
        } 
        
    printf ("%lld",s);
    
    return 0;
}