# coding: utf-8
import math

N = int(input())


def is_prime(num):
    if num < 2:
        return False
    if num == 2 or num == 3 or num == 5:
        return True
    if num % 2 == 0 or num % 3 == 0 or num % 5 == 0:
        return False

    # 疑似素数(2でも3でも5でも割り切れない数字)で次々に割っていく
    prime = 7
    step = 4
    num_sqrt = math.sqrt(num)
    while prime <= num_sqrt:
        if num % prime == 0:
            return False
        prime += step
        step = 6 - step

    return True


def make_prime_list(num):
    if num < 2:
        return []

    # 0のものは素数じゃないとする
    prime_list = [i for i in range(num + 1)]
    prime_list[1] = 0 # 1は素数ではない
    num_sqrt = math.sqrt(num)

    for prime in prime_list:
        if prime == 0:
            continue
        if prime > num_sqrt:
            break

        for non_prime in range(2 * prime, num, prime):
            prime_list[non_prime] = 0

    return [prime for prime in prime_list if prime != 0]


def solve():
    if N == 4:
        return 4
    
    if is_prime(N):
        return N
    N_sqrt = math.ceil(math.sqrt(N))
    primes = make_prime_list(N_sqrt)

    check_list = primes[:]
    
    for prime in primes:
        if prime * 2 > N_sqrt:
            break
        check_list.append(prime * 2)

    check_list.sort()

    for num in check_list:
        if num == 2:
            continue

        if N % num == 0:
            return num

    if N % 2 == 0:
        return N // 2


print(solve())