#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream f ( "fractii.in" );
ofstream g ( "fractii.out" );
bool v[1000001];
int phi[1000001];
void initphi ( int n )
{
    phi[1] = 0;

    for ( int i = 2; i <= n; i++ )
        phi[i] = i;
}
void ciur ( int N )
{
    v[1] = 1;

    for ( int i = 2; i <= N; i += 2 )
    {
        v[i] = 1;
        phi[i] /= 2;
    }

    for ( int i = 3; i <= N; i += 2 )
        if ( v[i] == 0 )
        {
            phi[i] = i - 1;

            for ( int j = 2 * i; j <= N; j += i )
            {
                phi[j] = phi[j] / i * ( i - 1 );
                v[j] = 1;
            }
        }
}
int main()
{
    int  n;
    long long nr = 1;
    f >> n;
    initphi ( n );
    ciur ( n );

    for ( int i = 2; i <= n; i++ )
        nr += phi[i];

    nr *= 2;
    g << nr - 1;
    return 0;
}