#include <iostream>
#include <fstream>
using namespace std;
int a[5000010],deq[5000010],i,n,k,ul,pr;
long long s;

ofstream g("deque.out");
int main()
{
    freopen("deque.in","r",stdin);
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
        scanf("%d",&a[i]);
    pr=1;
    ul=s=0;
    for(i=1;i<=n;i++)
    {
        while(pr<=ul&&a[i]<a[deq[ul]])
            ul--;
        deq[++ul]=i;
        if(deq[pr]==i-k)
            pr++;
        if(i>=k)
            s+=a[deq[pr]];
    }
    g<<s;
    return 0;
}