#include <bits/stdc++.h>

using namespace std;

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

long long n, k, s;
const int LMAX = 5000007;
int v[LMAX];
deque<int> dq;

int main()
{
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
    {
        fin >> v[i];
    }
    dq.push_back(1);

    for(int i = 2; i <= n; i++)
    {
        while(v[i] <= v[dq.back()] && !dq.empty())
        {
            dq.pop_back();
        }
        dq.push_back(i);

        if(i - dq.front() == 3)
        {
            dq.pop_front();
        }

        if(i >= k)
        {
            s += v[dq.front()];
        }
    }

    fout << s;

    return 0;
}