#include <bits/stdc++.h>

using namespace std;

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

const int nmax = 5e6 + 5;

deque <int> dq;

int n, k, v[nmax];

signed main()
{
    fin >> n >> k;
    for (int i = 1; i <= n; i++)
        fin >> v[i];
    long long sum = 0;
    for (int i = 1; i <= n; i++)
    {
        while (!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (i >= k)
        {
            while (!dq.empty() && i - dq.front() >= k)
                dq.pop_front();
            sum += v[dq.front()];
        }
    }
    fout << sum;
    return 0;
}