#include<fstream>

using namespace std;

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

unsigned long long solutie;
int n , frac[1000005];

int main(){
    fin >> n;
    for( int i = 1; i <= n; i++ ){
        frac[i] = i;
    }

    for( int i = 2; i <= n; i++){
        if( frac[i] == i )
            for( int j = i; j <= n; j += i ){
                frac[j] = ( frac[j]/i ) * (i - 1);
            }
    }

    solutie = 1;
    for( int i = 2; i <= n; i++ ){
        solutie += frac[i] * 2;
    }

    fout << solutie;
    return 0;
}