#include <bits/stdc++.h>

using namespace std;

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

const int nmax = 5000005;
int n, k;
int v[nmax];
deque <int> dq;

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