#include <bits/stdc++.h>
using namespace std;

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

int main()
{
    long long n, nr = 1;
    fin >> n;

    long long ciur[n + 1];
    for (long long i = 1; i <= n; i ++)
        ciur[i] = i;

    for (long long i = 2; i <= n; i ++)
        if (ciur[i] == i)
            for (long long j = i; j <= n; j += i)
                ciur[j] = ciur[j] * (i - 1) / i;

    for (long long i = 2; i <= n; i ++)
        nr += 2 * ciur[i];
    fout << nr;

    fin.close();
    fout.close();

    return 0;
}