import java.util.Scanner;

/**
 * Created by Radu on 4/17/2015.
 */
public class prog {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int d;
        if (n == 4) {
            System.out.println(2);
            System.exit(0);
        }
        for (d = 2; d <= Math.sqrt(n); d++) {
            if (n % d == 0) {
                break;
            }
        }
        if (d > Math.sqrt(n)) {
            System.out.println(n - 1);
        } else {
            System.out.println(0);
        }


    }
}