#include <bits/stdc++.h>

using namespace std;

int n,k,v[5000005],deq[5000005];
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",&v[i]);
    int Front=1,backT=0;
    for (int i=1;i<=n;++i)
    {
        while (Front<=backT && v[i]<=v[deq[backT]])
            --backT;
        deq[++backT]=i;
        if (deq[Front]==i-k)
            Front++;
        if (i>=k)
            s+=v[deq[Front]];
    }
    printf("%lld",s);
    return 0;
}