isPrime

import java.util.Arrays;
import java.util.Scanner;

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

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

        Boolean[] isPrime = new Boolean[n + 1];
        Arrays.fill(isPrime, true);

        for (int i = 2; i < Math.sqrt(n) + 1; i++) {
            if (isPrime[i]) {
                for (int j = i * i; j <= n; j += i) {
                    isPrime[j] = false;
                }
            }
        }

        for (int i = isPrime.length - 1; i > 0 ; i--) {
            if (isPrime[i]) { // not (!isPrime[i])
                System.out.println(i);
                return;
            }
        }
    }
}