#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

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

deque<int> deq, deq2; //deq - pozitia , deq2 - valoarea

int main()
{
    int n, k, x;
    f >> n >> k;

    long long s =0;
    for(int i=1; i<=n; i++)
    {
        f >>x;
        if(!deq.empty() && deq.front() <= i-k)
        {
            deq.pop_front();
            deq2.pop_front();
        }

        while(!deq2.empty()&& deq2.back()>=x)
        {
             deq.pop_back();
             deq2.pop_back();
        }
        deq.push_back(i);
        deq2.push_back(x);
        if (i>=k) s+=deq2.front();

    }
    g << s;

    f.close();
    g.close();

    return 0;
}