#include <iostream>
#include <fstream>

using namespace std;

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

long long form_calc (int x)
{
    long long aux=x;
    long long p=x;

    if (x%2==0)
    {
        p=(p/2);
        while (x%2==0)
            x=x/2;
    }

    for (int d=3; d*d<=aux; d+=2)
    {
        if (x%d==0)
        {
            p=(p/d)*(d-1);
            while (x%d==0)
                x=x/d;
        }
        d+=2;
    }
    if (x>1)
        p=(p/x)*(x-1);
    return p;
}

int main()
{
    long long x;
    long long sum=1;

    fin>>x;

    for (long long i=2;i<=x;i++)
    {
        sum+=2*form_calc(i);
    }
    fout<<sum;

    return 0;
}