#include <iostream>
#include <bits.h>
#include <deque>
#include <fstream>
#define N 500000
using namespace std;

int v[N], s;
deque <int> d;

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

int main()
{
    int i, n, k;
    in >> n >> k;
    //cin >> n >> k;
    for(i = 0; i < n; i++)
    {
        in >> v[i];
        //cin >> v[i];
        if(!d.empty() && d.front() == i - k)
        {
            d.pop_front();
        }
        while(!d.empty() && v[d.back()] >= v[i])
        {
            d.pop_back();
        }
        d.push_back(i);
        if(i >= k - 1)
        {
            s += v[d.front()];
        }
    }
    out << s;
    //cout << s;
    return 0;
}