#include <fstream>
#include <iostream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int a[5000000];
deque<int> dq;
int main()
{

    int n, k;
    fin >> n >> k;
    for (int i = 0; i < n; i++)
    {
        fin >> a[i];
    }
    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++)
    {
        int left = i - k + 1;

        while (!dq.empty() && a[dq.back()] >= a[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);

        if (dq.front() < left)
        {
            dq.pop_front();
        }
        // cout << a[dq.front()] << " ";
        sum += a[dq.front()];
    }
    fout << sum;
    return 0;
}