/*
https://infoarena.ro/problema/deque
*/
#include <fstream>
#include <deque>

using namespace std;

struct element
{
    int poz, val;
};

int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n, k;
    in >> n >> k;
    deque <element> dq;
    long long s = 0;
    for (int i = 0; i < n; i++)
    {
        element x;
        in >> x.val;
        x.poz = i;
        while (!dq.empty() && x.val <= dq.back().val)
        {
            dq.pop_back();
        }
        if (!dq.empty() && dq.front().poz == i - k)
        {
            dq.pop_front();
        }
        dq.push_back(x);
        if (i >= k - 1)
        {
            s += dq.front().val;
        }
    }
    out << s << "\n";
    in.close();
    out.close();
    return 0;
}