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

using namespace std;

int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");

    int n, k;
    in >> n >> k;

    vector<int> a(n);
    for (int i = 0; i < n; i++)
    {
        in >> a[i];
    }

    deque<int> dq;
    for (int i = 0; i < k; i++)
    {
        while (!dq.empty() && a[dq.back()] >= a[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
    }

    long long sum = a[dq.front()];
    for (int i = k; i < n; i++)
    {
        if (dq.front() <= i - k)
        {
            dq.pop_front();
        }
        while (!dq.empty() && a[dq.back()] >= a[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        sum += a[dq.front()];
    }

    out << sum << endl;

    in.close();
    out.close();
    return 0;
}