#include<stdio.h>
int f,b,n,i,k;
long long rez=0;
int a[5000001],deq[5000001];
int main(void)
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
        scanf("%d",&a[i]);
    f=1;
    b=0;
    for(i=1;i<=n;i++)
    {
        while(f<=b && a[i]<=a[deq[b]]) b--;
        deq[++b]=i;
        if(deq[f]==i-k)
            f++;
        if(i>=k)
            rez+=a[deq[f]];
    }
    printf("%lld",rez);
    return 0;
}