#include<stdio.h>
int N,K,a[5000050],d[5000050];
long long s;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&N,&K);
    for(int i=1;i<=N;++i)
        scanf("%d",&a[i]);
    int f=1;
    int b=0;
    for(int i=1;i<=N;++i)
    {
        while((f<=b)&&(a[i]<=a[d[b]]))
            --b;
        ++b;
        d[b]=i;
        if(d[f]==i-K)
            ++f;
        if(i>=K)
            s=s+a[d[f]];
    }
    printf("%lld",s);
}