def main():
    n = int(input())

    d = 3
    while d * d <= n:
        if n % d == 0:
            print(d)
            break
        d += 1
    else:
        if n % 2 == 0 and n // 2 != 2:
            print(n//2)
        else:
            print(n)


if __name__ == '__main__':
    main()