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

struct ep{
    int elem;
    int poz;

};
deque <ep> deq;
long long int suma;
long long int n,k;


int main()
{
    fin >> n>> k;
    ep e;

    for(long long int i=0;i<n;i++)

    {
        e.poz=i;
        fin >> e.elem;

        while(!deq.empty() && e.elem<deq.back().elem)
            deq.pop_back();
        deq.push_back(e);
        if(!deq.empty() && i-deq.front().poz==k)
            deq.pop_front();
        if(i>=k-1)
        {
            suma+=deq.front().elem;
        }




    }
        fout << suma;

}