#include<fstream>
#define Max 1000000
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
int phi[1000001],i,j,n;
long long sum;
int main(){
   fin>>n;
   sum=1;
   for (i=1;i<=n;i++)
    phi[i]=i;
   for (i=2;i<=n;i++){
    if (phi[i]==i)
        for (j=i;j<=n;j+=i)
          phi[j]=phi[j]/i*(i-1);
    sum=sum+(long long)2*phi[i];
   }
   fin.close();
   fout<<sum;
   fout.close();
   return 0;
}