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

using namespace std;

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

deque <int> mydeque;

int main()
{   int i, v[500004], n, k, s = 0, j;

    f>>n>>k;

    for(i = 1; i <= n; i++)

        f>>v[i];


    for(i = 1; i <= n; i++){

        while(!mydeque.empty() && v[i] <= v[mydeque.back()])

            mydeque.pop_back();


        mydeque.push_back(i);

         if(i >= k) {

            s += v[mydeque.front()];
//            cout<<v[mydeque.front()]<<" ";

            if(mydeque.front() == i - k + 1)

                mydeque.pop_front();


    }
    }










    g << s;



    return 0;
}