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