primes = [2]

for i in range(3, 2000000, 2):
    if len(primes) == 20:
        break
    for p in primes:
        if i % p == 0:
            break
        if p * p > i:
            primes.append(i)
            break

n = int(input())

for p in primes:
    if n % p != 0:
        print(p)
        break