import java.util.Scanner;

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

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

        Boolean[] isPrime = new Boolean[n];
        for (int i = 0; i < isPrime.length; i++) {
            isPrime[i] = false;
        }

        for (int i = 2; i <= n ; i++) {
            int count = 0;
            for (int j = 1; j <= i ; j++) {
                if (i % j == 0) {
                    count++;
                }
            }
            if (count == 2) {
                isPrime[i - 2] = true;
            }
        }

        for (int i = isPrime.length - 1; i > 0 ; i--) {
            if (!isPrime[i]) {
                continue;
            }
            System.out.println(i + 2);
            return;
        }
    }
}