#include <iostream>
#include <fstream>
using namespace std;
///Determinati nr. de fractii ireductibile cu numitorul si numaratorul mai mici decat un nr. n;

long long v[1000001],u[1000001];
int main()
{
    ifstream fin ("fractii.in");
    ofstream fout ("fractii.out");
    long long n,s=-1;
    fin>>n;
    for (int i=0; i<=n; i++)
    {
        u[i]=i;
    }
    for (int i=2; i<=n; i+=2)
    {
        if (i!=2)
        v[i]=1;
        u[i]=u[i]/2*1;
    }
    for (int i=3; i<=n; i+=2)
    {
        if (!v[i])
        for (int j=i; j<=n; j+=i)
        {
            if (j!=i)
            v[j]=1;
            u[j]=u[j]/i*(i-1);
        }
    }
    for (int i=0; i<=n; i++)
       {
            s+=2*u[i];
       }
        fout<<s;
        fout.flush();
}