import java.util.*;
import java.io.*;
import java.math.*;

public class No312 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long n = sc.nextLong();
		for(long i = 3; i < n; i++) {
			if(isPrime(i)) {
				if(n%i == 0) {
					System.out.println(i);
					return;
				}
			}
		}
	}
	public static boolean isPrime(long num) {
        if (num < 2) return false;
        else if (num == 2) return true;
        else if (num % 2 == 0) return false;
        
        double sqrtNum = Math.sqrt(num);
        for (int i = 3; i <= sqrtNum; i += 2) {
            if (num % i == 0) {
                return false;
            }
        }
        return true;
    }
}