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

int main()
{
    std::ifstream f1("deque.in");
    std::ofstream f2("deque.out");
    long long int n, k, x, S = 0, cnt = 0;
    std::deque<long long int> poz;
    std::deque<long long int> rez;
    f1 >> n >> k;

    while(f1 >> x)
    {
        if((!rez.empty())&&(cnt - k >= poz.front()))
        {
            rez.pop_front();
            poz.pop_front();
        }

        if(!rez.empty())
            while(!rez.empty() && x <= rez.back())
            {
                rez.pop_back();
                poz.pop_back();
            }

        rez.push_back(x);
        poz.push_back(cnt);

        if(cnt >= k-1)
        {
            S += rez.front();
        }
        cnt++;
    }
    f2 << S;
}