import math

def find_smallest_prime_factor(d):
    if d % 2 == 0:
        return 2
    max_divisor = int(math.isqrt(d)) + 1
    for i in range(3, max_divisor, 2):
        if d % i == 0:
            return i
    return d  # d is prime

def main():
    N = int(input().strip())
    if N % 2 == 0:
        d = N
        while d % 2 == 0:
            d //= 2
        if d == 1:
            print(4)
        else:
            print(find_smallest_prime_factor(d))
    else:
        print(find_smallest_prime_factor(N))

if __name__ == "__main__":
    main()