#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fractii.in");
ofstream out("fractii.out");

const int MAXN = 1000000;
long long phi[MAXN+1], isPrime[MAXN+1];
long long N;

void citire(){
    in>>N;
}

void ciurEratostene(){

    for(int i = 2; i <= MAXN; i++)
        for(int j = 2*i; j <= MAXN; j += i)
            isPrime[ j ] =1;
}

void calculeazaTotient(){

    for(int i = 1; i <= MAXN; i++)
        phi[ i ] = i;

    for(int i = 2; i <= MAXN; i++)
        if( isPrime[ i ] == 0 )
            for(int j = i; j <= MAXN; j += i){

                    phi[ j ] = (long long) phi[ j ]*( i - 1 );
                    phi[ j ] = (long long) phi[ j ]/i;
            }
}

long long calculeazaFormula(long long n){

    long long answer = 1;

    for(int i = 2; i <= n; i++)
        answer += (long long) 2*phi[ i ];

    return answer;
}

int main(){

    citire();
    ciurEratostene();
    calculeazaTotient();
    out<<calculeazaFormula(N);
    return 0;
}