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();

    }

}