#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

int n, k, x, sum;
deque<pair<int, int>> dq;

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