import java.util.Scanner;

public class No312 {

	public static void main(String[] args) {

		Scanner s = new Scanner(System.in);
		
		long n = s.nextLong();
		
		long i = 3;
		double sqrt = Math.sqrt(n);
		
		if (i > sqrt) {
			i = n;
		}
		else {
			while (i < sqrt) {
				
				if ((n % i) == 0) break;
				i++;
			}
			if (i == Math.ceil(sqrt)) i = n;
		}
		
		System.out.println(i);
	}
}