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

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

#define nmax 5000005

deque <long long> Deck;

long long n,k,v[nmax],sum=0;

int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
        while(Deck.size()>0 && v[i]<=v[Deck.back()])
            Deck.pop_back();
        Deck.push_back(i);
        if(Deck.front()==i-k)
            Deck.pop_front();
        if(i>=k)
            sum+=v[Deck.front()];
    }
    fout<<sum;
}