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

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int main()
{
    deque<int> dq;
    int n, i, m;
    long long sum;
    int lista[50000010];
    fin >> n >> m;



    for (i = 0; i < n; i++)
        fin >> lista[i];

    fin.close();

    for (i = 0; i < n; i++){
        while (dq.size() != 0 && lista[i] <= lista[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front() < (i - m + 1))
            dq.pop_front();
        if(i >= m-1)
            s += lista[dq.front()];
    }

    fout << s;

    fout.close();
    return 0;
}