#include <iostream>
#include <fstream>
#include <algorithm>
#include <deque>
#include <limits>

using namespace std;

int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    int n, k, sum = 0;
    f >> n >> k;
    deque<int> d;
    for (int i = 0; i < n-1; i++)
    {
        int num;
        f >> num;
        d.push_back(num);
        if (static_cast<int>(d.size()) > k)
        {
            d.pop_front();
        }
        if (static_cast<int>(d.size()) == k)
        {
            int min = *min_element(d.begin(), d.end());
            sum += min;
        }
    }
    g << sum;
    f.close();
    g.close();

    return 0;
}