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 - 1];
        for (int i = 0; i < isPrime.length; i++) {
            isPrime[i] = true;
        }


        for (int i = 0; i < Math.sqrt(n) + 2; i++) {
            int startingPrime = i + 2;
            if (isPrime[i]) {
                for (int j = startingPrime * startingPrime; j <= n; j+= startingPrime) {
                    isPrime[j - 2] = false;
                }
            }

        }

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