#include <fstream>   
  
using namespace std;   
  
#define N_MAX 1000000   
#define FIN "fractii.in"   
#define FOUT "fractii.out"   
int phi[N_MAX],n;   
  
int main()   
{   
    int k,i,j;
	double s = 1;   
    fstream fin(FIN);   
    ofstream fout(FOUT);   
  
    fin >> n;   
       
    //calculate phi function   
    for(i = 1; i <= n; ++i)   
        phi[i] = i-1;   
       
    for(i = 2; i <= n; ++i)   
        for(j = 2 * i; j <= n; j+= i)   
            phi[j] -= phi[i];   
       
    for(k = 2; k <= n; ++k)   
        s += 2 * phi[k];   
  
    fout << s;
       
    return 0;   
}