#include <string.h>
#include <deque>
#include <fstream>
#include <iostream>

using namespace std;

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

/*
 *
 */

deque <pair <int, int>> dq;

int main ()
{
    int n, k;
    int sum = 0;
    fin >> n >> k;
    for(int i = 0; i < n; i++)
    {
        int x;
        fin >> x;
        while(!dq.empty() && dq.front().second <= i - k)
        {
            dq.pop_front();
        }
        while(!dq.empty() && x < dq.back().first)
        {
            dq.pop_back();
        }
        dq.push_back(make_pair(x, i));
        if(i >= k - 1)
            sum += dq.front().first;
    }
    fout << sum;
    return 0;
}