#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int main()
{
    int v[5000001], coada[5000001], inceput, sfarsit, n, k, i;
    long suma=0;
    f>>n>>k;

    for(i=0;i<n;i++)
        f>>v[i];
    inceput=0;
    sfarsit=-1;
    for(int i=0;i<n;i++)
    {
        while(inceput<=sfarsit && v[i]<v[coada[sfarsit]])
        {
            sfarsit--;
        }
        coada[++sfarsit] = i;

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

        if(i>=k-1) suma+=v[coada[inceput]];
    }

    g<<suma;

}