#include <fstream>
#include <bitset>
#include <vector>
#include <algorithm>
#define pb push_back
#define int long long
using namespace std;
ifstream cin("fractii.in");
ofstream cout("fractii.out");
using pii = pair<int,int>;
const int nmax = 1e6 + 1;
int n;
bitset<nmax>b;
vector<int>primes;
int phi[nmax], sum, sz;
signed main()
{
    cin >> n;
    sum = 1;
    for(int i = 2 ; i <= n ; i++)
    {
        if(!b[i])
        {
            primes.pb(i);
            phi[i] = i - 1;
            ++sz;
        }
        sum += phi[i]*2;
        for(int j = 0 ; j < sz && primes[j]*i <= n ; j++)
        {
            b[i*primes[j]] = 1;
            if(i%primes[j]==0)
            {
                phi[i*primes[j]] = phi[i]*primes[j];
                break;
            }
            else phi[i*primes[j]] = phi[i]*phi[primes[j]];
        }
    }
    cout << sum ;
    return 0;
}