//package fractii;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;

public class Main {

	public static void main (String[] args) throws IOException {
		
		Scanner scanner = new Scanner (new FileInputStream("fractii.in"));
		PrintWriter writer = new PrintWriter ("fractii.out");
		
		int n, i, j;
		long vector[] = new long[1000000];
		long suma = 0;
		n = scanner.nextInt();
		
		for (i = 1; i <= n; i++) {
			vector[i] = i;
		}
		for (i = 2; i <= n; i++) {
			if (i == vector[i]) {
				for (j = i; j <= n; j += i) {
					vector[j] = vector[j]/i * (i-1);
				}
			}
			suma += vector[i];
		}
		suma = suma * 2 + 1;
		writer.write(String.valueOf(suma));
		
		scanner.close();
		writer.close();
		
	}
	
}