#include <iostream>

#include <fstream>

#include <vector>

#include <deque>





using namespace std;





vector <int> numbers (5000003);

int N,K, i;

long long sum;



ifstream fin;

ofstream fout;





int main(void){

    deque <int> Deque;



    fin.open("deque.in");

    fin>>N>>K;

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

        fin>>numbers[i];

    fin.close();



    Deque.push_front(1);



    for (i=2; i<K; i++){

        while (numbers[Deque.front()] >= numbers[i] && Deque.size() > 0) Deque.pop_front();

        Deque.push_front(i);

    }









    for (i=K; i<=N; i++){

        while (numbers[Deque.front()] >= numbers[i] && Deque.size() > 0) Deque.pop_front();

        Deque.push_front(i);

        sum += ((long long)numbers[Deque.back()]);



        if (Deque.back() == i - K + 1 ) Deque.pop_back();

    }



    fout.open("deque.out");

    fout<<sum<<"\n";

    fout.close();



    return 0;

}