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