#include <bits/stdc++.h>

using namespace std;
deque< pair <int, int> >coada;
int main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");

    long long n, k, x, sum = 0;
    cin >> n >> k;
    for(int i = 1; i < k; i ++)
    {
        cin >> x;
        while (!coada.empty() && x <= coada.back().first)
        {
            coada.pop_back();
        }
        coada.push_back(make_pair(x, i));
    }
    for (int i = k; i <= n; ++i)
    {
        cin >> x;
        while (!coada.empty() && x <= coada.back().first)
        {
            coada.pop_back();
        }
        coada.push_back(make_pair(x, i));
        while (coada.front().second <= i - k)
        {
            coada.pop_front();
        }
            sum += coada.front().first;
    }
    cout << sum;
    return 0;
}