#include <fstream>
#include <cmath>

#define N 1000000
using namespace std;
ifstream in("fractii.in");
ofstream out("fractii.out");

long long phi[1000000];
int main()
{
    int i,j,n;
    long long s;
    in>>n;
    for (int i=1;i<=n;i++) phi[i]=i;

for (int i=2;i<=n;i++)
   if (phi[i]==i)
      for (j=i;j<=n;j+=i){ phi[j] /=i, phi[j] *= (i-1);}
        s=1;
    for(i=2;i<=n;i++)
     {
        s=s+2*phi[i];
     }
    out<<s;
    return 0;
}