#include<bits/stdc++.h>
using namespace std;
#define int long long
using ll = long long;
const int nn = 1e6 + 5;
bool t[nn];
int phi[nn];
vector<int> p;
signed main()
{
    phi[1] = 1;
    int n;
    cin >> n;
    int aw = 0;
    for (int i = 2; i <= n; i++)
    {
        if (!t[i])
        {
            phi[i] = i - 1;
            p.push_back(i);
        }
        for (int j = 0; p[j] <= n / i; j++)
        {
            t[p[j] * i] = true;
            if (i % p[j] == 0)
            {
                phi[p[j] * i] = phi[i] * p[j];
                break;
            }
            phi[p[j] * i] = phi[i] * (p[j] - 1);
        }
    }
    for (int i = 1; i <= n; i++)
        aw += phi[i];
    cout << aw;
}