#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

const int NMAX = 5000000;

int n, k, v[NMAX + 1];
long long suma;
deque<int> dq;

int main()
{
    int i;
    f >> n >> k;
    for(i = 1; i <= k; ++i)
    {
        f >> v[i];
        while(!dq.empty() && v[i] < v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
    }
    suma += v[dq.front()];
    for(i = k + 1; i <= n; ++i)
    {
        f >> v[i];
        while(!dq.empty() && v[i] < v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i - k == dq.front())
            dq.pop_front();
        suma += v[dq.front()];
    }
    g << suma;
    f.close();
    g.close();
    return 0;
}