import java.math.BigInteger;
import java.util.*;
import java.util.stream.Collectors;

public class test {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int n = Integer.parseInt(scanner.nextLine());
        int primeNum = 0;

        for (int i = 1; i <= n ; i++) {
            int counter = 0;
            for (int j = 1; j <= i ; j++) {
                if (i % j == 0) {
                    counter++;
                }
                if (counter > 2) {
                    break;
                }
            }
            if (counter == 2) {
                primeNum = i;
            }
        }
        System.out.println(primeNum);
    }
}