#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
long long int p,n,a[1000000],b[1000000],i,j,k;
int phi(int n)
{
    int sol=n;
    for(int i=2;i<=(int)sqrt(n);i++)
    {
        if(n%i==0)
            {sol=sol-sol/i;
             n=n/i;}
             while(n%i==0)
                n=n/i;
    }
      if(n>1)
            sol=sol-sol/n;
      return sol;
}
int main()
{
    fin>>n;
    for(i=2;i<=n;i++)
    {
        if(a[i]==0)
        for(j=2*i;j<=n;j=j+i)
            a[j]=1;
    }
    p=3;
    for(i=3;i<=n;i++)
        {if(a[i]==0)
        b[i]=i-1;
        else
        b[i]=phi(i);
        p=p+b[i]*2;}
        fout<<p;
    return 0;
}