#include <bits/stdc++.h>
using namespace std;

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

int n;
long long phi[1000005];
long long sum=1;

int main()
{
    f >> n;
    for (int i=2;i<=n;i++) {
        phi[i]=i;
    }
    for (long long i=2;i<=n;i++) {
        if (phi[i]==i) {
            phi[i]--;
            for (int j=2*i;j<=n;j+=i) {
                phi[j] = phi[j]*(i-1)/i;
            }
        }
    }
    for (int i=2;i<=n;i++) {
        sum += phi[i]*2;
    }
    g << sum;
    return 0;
}