#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int a[5000000];
int main()
{
    int n, k, s = 0;
    fin >> n >> k;
    for(int i = 0; i < n; i++)
        fin >> a[i];

    deque <int> dq;

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

        dq.push_back(i);
        if(i - k >= dq.front())
            dq.pop_front();

        if(k - 1 <= i)
            s += a[dq.front()];
    }
    fout << s;
    return 0;
}