#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");


struct aragaz
{
    int poz;
    int val;
};

int n,k;
int z;
deque<aragaz> dq;
int main()
{
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
    {
        int a;
        fin >> a;
        while (!dq.empty() && dq.back().val > a)
        {
            dq.pop_back();
        }
        dq.push_back({i,a});
        while (!dq.empty() && dq.front().poz == i - k)
        {
            dq.pop_front();
        }
        if (i >= k && n >= i)
            z += dq.front().val;
    }
    fout << z;
    return 0;
}