package laugh;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class BiggestPrimeNumber {
    static boolean isPrime(int n)
    {

        if (n <= 1)
            return false;


        for (int i = 2; i < n; i++)
            if (n % i == 0)
                return false;

        return true;
    }


    static void printPrime(int n)
    {
        List<Integer> add = new ArrayList<Integer>();



        for (int i = 2; i <= n; i++)
        {
            if(isPrime(i)){
                add.add(i);
            }

        }

        System.out.println( Collections.max(add));

    }


    public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);
        int n = Integer.parseInt(in.nextLine());
        printPrime(n);
    }
}