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