#include <iostream>

#include <fstream>



using namespace std;

ifstream f("deque.in");

ofstream g("deque.out");



int a[5000001], b[5000001], n, k, p, u, i;

long long s;



int main()

{

    f>> n >> k;



    for(i = 1; i <= n; i++)

        f>>a[i];



    p = 1;



    for(i = 1; i <= n; i++)

    {

        while(p <= u && a[i] < a[b[u]])

            u--;

        b[++u] = i;

        if(b[p] == i - k)

            p++;

        if(i >= k)

            s = s + a[b[p]];

    }



    g<< s;



    return 0;

}