package no312;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long n = sc.nextLong();
		n = 499999999979L * 2;
		//3以上の最小の約数
		long max = (long) Math.sqrt(n);
		for(long i=3;i<=max;i++) {
			if (n % i == 0) {
				System.out.println(i);
				return;
			}
		}
		if (n % 2 == 0) {
			System.out.println(n / 2);
			return;
		}
		System.out.println(n);
	}
}