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

deque<int> dq, pq;
long long n, k, x, sum=0 ;

void ins(int x, int i)
{
    if (!dq.empty() && pq.front()<=i-k)
    {
        dq.pop_front();
        pq.pop_front();
    }
    while (!dq.empty() && dq.back()>=x)
    {
        dq.pop_back();
        pq.pop_back();
    }

    dq.push_back(x);
    pq.push_back(i);
    return;
}

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

    f >> n >> k;
    for(int i=1; i<=n; i++)
    {
        f >> x;
        ins(x, i);
        if (i>=k) sum=sum+dq.front();
    }

    g << sum;

    f.close();
    g.close();
    return 0;
}