import math

def is_prime(num):
    if num < 2:
        return False
    for i in range(2, int(math.sqrt(num))+1):
        if num % i == 0:
            return False
    return True

n = int(input())

for i in range(n//2, 1, -1):
    if n % i == 0 and is_prime(i):
        print(i)
        break