#include <bits/stdc++.h>
#define LL long long

using namespace std;

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

LL phi[1000005];
LL n, sol;

int main ()
{
    fin>>n;
    for(LL i=1; i<=n; i++)
        phi[i]=i;

    sol=1;
    for(LL i=2; i<=n; i++)
    {
        if(phi[i] == i)
            for(LL j=i; j<=n; j+=i)
                phi[j] = phi[j] / i * (i-1);
        sol += 2*phi[i];
    }
    fout<<sol;
    return 0;
}