#include <fstream>
#include <iostream>
#include <deque>

using namespace std;

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

const int NMAX = 5e6;
const int MIN = -1e7;

int v[NMAX+1], coada[NMAX+1];


int main()
{
    int n, k;
    f>>n>>k;
    long long int sum = 0;
    coada[0] = MIN;
    int in = 1;
    int sf = 1;
    for(int i=1; i<=n; i++){
        f>>v[i];
        if( i>= k and i-k >= coada[in])
            in ++;
        while(in <= sf and v[i] < v[coada[sf]])
            sf --;
        sf ++;
        coada[sf] = i;
        if(in <= sf and i >= k)
            sum += v[coada[in]];
    }
    g<<sum;

    return 0;
}