include<iostream>
#include<fstream>
#include<cmath>
#include<algorithm>
#define ull unsigned long long int
#define DM 1000000
using namespace std;

ifstream f("fractii.in");
ofstream g("fractii.out");

ull numara(int n)
{
    int F[n+1];
    for(int i=1;i<=n;++i)F[i]=i;
    for(int i=2;i<=n;++i)
        if(F[i]==i)
        {
            F[i]--;
            for(int j=2;i*j<=n;++j)
                F[i*j]=F[j*i]/i*(i-1);
        }
        
    ull q=1;
    for(int i=2;i<=n;++i)
        q+=2*F[i];
    return q;
}

int main()
{
    int x;f>>x;
    f.close();
    g<<numara(x)<<'\n';
    g.close();
    return 0;
}