#include <stdlib.h>
#include <stdio.h>
long long int p, n, b[1000000], i, j, k;
int main(){
	freopen( "fractii.in", "r", stdin);
	freopen("fractii.out", "w", stdout);
	scanf("%lli", &n);

	for (i = 2; i <= n; i++){
		b[i] = i;
	}
	for (i = 2; i <= n; i++){
		if (b[i] == i){
			b[i] = i - 1;
			for (j = 2 * i; j <= n; j = i + j){
				b[j] = b[j] - b[j] / i;
			}
		}
	}
	p = 3;
	for (i = 3; i <= n; i++){
		p = p + 2 * b[i];
	}
	printf("%lli", p);

	return 0;
}