#include <iostream>

using namespace std;



int main()
{
	freopen("fractii.in", "r", stdin);
	freopen("fractii.out", "w", stdout);

	int n;
	cin >> n;

	int *v = (int *)calloc(n, sizeof(int));
	long long nr = 0;
	int *phy = (int *) calloc(n, sizeof(int));

	for (int i = 0; i < n; i++)
		phy[i] = i;

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

		nr += phy[i];
	}

	cout << nr * 2;
}