#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define MAXN 1000001

int n;
long long ciur[MAXN];

void init_ciur(int val) {
	for (int i = 0; i <= n; i++) {
		ciur[i] = val;
	}
}

void make_fi_of_n_ciur() {
	for (int i = 2; i <= n; i++) {
		if (ciur[i] & 1) {
			ciur[i] = i - 1;
			for (int pos = i << 1; pos <= n; pos += i) {
				long long aux = pos / i;
				ciur[pos] *= (i - 1);
				while (aux % i == 0) {
					ciur[pos] *= i;
					aux /= i;
				}
			}
		}
	}
}

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

	scanf("%d", &n);

	init_ciur(1);

	make_fi_of_n_ciur();

	long long sum = 1;
	for (int i = 2; i <= n; i++) {
		sum += 2*ciur[i];
	}
	printf("%lld\n", sum);

	return 0;
}