#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
int n;
bool val[1000001];
int phi[1000001];
long long calcphi(int n)
{
    int i,j;
    for(i=1;i<=n;i++)phi[i]=i-1;
    phi[1]=1;
    for(i=2;i<=n;i++)
        if(!val[i])for(j=2;i*j<=n;j++){phi[i*j]-=j-1;val[i*j]=1;}
    long long s=0;
    for(i=1;i<=n;i++)s+=phi[i];
    s=s*2-1;
    return s;
}
int main()
{
    f>>n;
    g<<calcphi(n);
    return 0;
}