#include<iostream>
#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
    int n, k;
    int s=0;
    f>>n>>k;
    int *d = new int[5000001], *a = new int[5000001];
    int st =  1, dr = 0;

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


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

        while(a[i] <= a[d[dr]] && st <= dr)
            dr--;

        dr++;
        d[dr] = i;


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

        if(i >= k)
            s += a[d[st]];
    }
    g<<s;
    return 0;
}