#include<stdio.h>
int deq[5000100], t[5000100];
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,i,down=0,up=0,k;
    long long s=0;
    scanf("%d%d",&n,&k);

    t[0] = -2000000000;
    deq[0]=0;
    down = 1;

    for(i=1;i<=n;i++)
    {
        scanf("%d",&t[i]);
        while(t[i]<t[deq[up]]&&up>=down)
            up--;
        deq[++up]=i;
        while(deq[down]<=i-k && up>=down)
            down++;
        if(i>=k)
            s+=t[deq[down]];

    }
    printf("%lld\n",s);
    return 0;
}