#include <fstream>
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
int n;
long long phi[1000001];
int main()
{
    fin >> n ;
    long long suma=1;
    for (int i=1; i<=n; i++) phi[i]=i;
    for ( int i=1;i<=n;i++)
        phi[i]=i-1;
    for ( int i=2;i<=n;i++)
        for ( int j=2*i;j<=n;j+=i)
            phi[j]-=phi[i];
    for( int i = 2 ; i <= n ; ++i )
        suma += 2*phi[i];
    fout << suma;
    return 0;
}