#include <iostream>
#include <fstream>
using namespace std;

#define maxN 5000005

ifstream f("deque.in");
ofstream g("deque.out");

int n,k,v[maxN],d[maxN];
long long s=0;

int main()
{
    int i,p,q;
    f>>n; f>>k;

    for(i=1; i<=n ;i++)
        f>>v[i];

    p=1;
    q=0;
    for(i=1; i<=n ;i++)
    {
        while( p<=q && v[i]<=v[d[q]] ) q--;

	d[++q]=i;

        if(d[p]==i-k) p++;

        if(i>=k) s+=v[d[p]];
    }
    g<<s;

    return 0;
}