#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

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


int n, k;
long long suma;
deque<pair<int, int>> dq;

int main()
{
    int i, x;
    f >> n >> k;
    for(i = 1; i <= k; ++i)
    {
        f >> x;
        while(!dq.empty() && x < dq.back().first)
            dq.pop_back();

        dq.push_back({x, i});
    }

    suma += dq.front().first;

    for(i = k + 1; i <= n; ++i)
    {
        f >> x;
        while(!dq.empty() && x < dq.back().first)
            dq.pop_back();

        dq.push_back({x, i});

        if(i - k == dq.front().second)
            dq.pop_front();

        suma += dq.front().first;
    }
    g << suma;
    f.close();
    g.close();
    return 0;
}