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

using namespace std;

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

deque<int> deck;
int n, k, v[5000005],s,dback,dfront;

int main()
{
    f >> n >> k;
    for (int i=1; i<=n; i++)
    {
        f >> v[i];
        if (i<k)
            deck.push_back(i);
    }
    for (int i=k; i<=n; i++)
    {
        if (!deck.empty()){
        while (v[deck.back()]>v[i] && !deck.empty())
        {
            deck.pop_back();
        }
        }
        deck.push_back(i);
        dback=deck.back();
        dfront=deck.front();
        if (deck.back()-deck.front()>=k)
            deck.pop_front();
        if (i>=k)
            s+=v[deck.front()];
    }
    g << s;
    return 0;
}