# -*- coding: utf-8 -*-

N = int(input())

i = 3
is_prime = True
while i*i<=N:
    if N%i == 0:
        is_prime = False
        break
    i += 1

if is_prime:
    if N%2 == 0:
        if N//2==2:
            print(N)
        else:
            print(N//2)
    else:
        print(N)
else:
    print(i)