#include<fstream>
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
unsigned long long sol;
int n,p[1000005];
int main(){
    fin>>n;
    for( int i = 1; i <= n; i++ ){
        p[i] = i;
    }
    for( int i = 2; i <= n; i++){
        if( p[i] == i )
            for( int j = i; j <= n; j += i ){
                p[j] = ( p[j]/i ) * (i - 1);
            }
    }
    sol = 1;
    for( int i = 2; i <= n; i++ ){
        sol += p[i] * 2;
    }
    fout << sol;
    return 0;
}