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

using namespace std;

deque <int > deq;
vector <int> v1;
int n,k ;

void citire()
{
    ifstream in("deque.in");
    in>>n>>k;

    int x;

    for(int i = 0 ; i < n ; i++)
    {
        in>>x;
        v1.push_back(x);
    }

    in.close();



}

int main()
{
int sum = 0 ;

citire();


    for(int i = 0 ; i < n ; i++)
    {
        while ( !deq.empty() && v1[deq.back()] <= v1[i])
            deq.pop_back();

        deq.push_back(i);

        if(deq.front() ==  i - k )
            deq.pop_front();

        if(i >= k - 1  )
            sum+= v1[deq.front()];


    }


cout<<sum<<endl;





    return 0;
}