#include<fstream>
using namespace std;

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

const int N=1000001;
int v[N];
int n;

int main()
{
    int i,j,sol;

    in>>n;

    v[1] = 1;
    for(i=2; i<=n; ++i) v[i] = i;

    sol = 1;
    for(i=2; i<=n; ++i)
    {
        if(v[i] == i)
        {
            for(j=i*2; j<=n; j+=i)
                v[j] = v[j] * (i-1) / i;
            --v[i];
        }

        ///out<<"v["<<i<<"] = "<<v[i]<<"\n";

        sol += v[i]*2;
    }
    ///sol = sol - 1;

    out<<sol;

    return 0;
}