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

using namespace std;

int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    int n, k, sum=0;
    f>>n>>k;
    deque<int> d;
    deque<int> dmin;

    for (int i=0; i<n; i++)
    {
        int num;
        f>>num;
        d.push_back(num);

        if (!dmin.empty() && dmin.front()<=i-k)
            dmin.pop_front();

        while (!dmin.empty() && d[dmin.back()]>num)
            dmin.pop_back();

        dmin.push_back(i);

        if (i>=k-1)
            sum+=d[dmin.front()];
    }

    g<<sum;
    f.close();
    g.close();

    return 0;
}