#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long n, k, s, i, v[5000005];
deque <long long> dq;
int main()
{
    fin >> n >> k;
    for (i = 1; i <= n; i++)
        fin >> v[i];
    dq.push_back(1);
    for (i = 2; i <=n; i++)
    {
        while (v[i] < v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (i >= k)
        {
            if (i - dq.front() == k)
                dq.pop_front();
            s += v[dq.front()];
        }
    }
    fout << s;
    return 0;
}