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


int n, k;
int v[5000000], coada[5000000];
int fata, spate;
long s;

int main()
{
    //ifstream f("numere.in");
    //ofstream g("numere.out.c");
    int i;

    cin>>n>>k;

    for(i = 1; i<= n; i++)
        cin>>v[i];
    fata = 1;
    spate = 0;

    for(i = 1; i<= n; i++)
    {
        while (fata <= spate && v[i] < v[coada[spate]])
            spate --;

        spate++;
        coada[spate] = i;

        if(coada[fata] == i-k)
            fata++;

        if( i>= k)
            s += v[coada[fata]];
    }
    cout<<s;
    return 0;
}