import java.util.*;


class BiggestPrimeNumber {
    /*
    Write a program that finds all prime numbers in the range 1 ... N. Use the Sieve of Eratosthenes algorithm.
    The program should print the biggest prime number which is <= N.

    Input
    On the first line you will receive the number N

    Output
    Print the biggest prime number which is <= N

    SIEVE PSEUDOCODE:
    input: an integer n > 1.
    output: all prime numbers from 2 through n.

    let A be an array of Boolean values, indexed by integers 2 to n, initially all set to true.
        for i = 2, 3, 4, ..., not exceeding √n do
            if A[i] is true
                for j = i2, i2+i, i2+2i, i2+3i, ..., not exceeding n do
                    A[j] := false

    return all i such that A[i] is true.
    */

    public static int sieveOfEratosthenes(int n) {
        // Initializing the array and setting all values to true:
        boolean[] primes = new boolean[n + 1];
        Arrays.fill(primes, true);

        for (int i = 2; i <= Math.sqrt(n); i++) {
            // If primes[i] is not changed to false, then it is a prime:
            if (primes[i]) {
                // Update all multiples of p to false:
                for (int j = i * i; j <= n; j += i)
                    primes[j] = false;
            }
        }

        // Iterating through the bool array backwards and returning the index of the first prime:
        for (int i = primes.length - 1; i >= 0; i--) {
            if (primes[i]) return i;
        }

        return 1;
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print(BiggestPrimeNumber.sieveOfEratosthenes(scanner.nextInt()));
    }
}