def factorial(n):
    """Compute factorial of n."""
    if n <= 1:
        return 1
    result = 1
    for i in range(2, n + 1):
        result *= i
    return result

if __name__ == "__main__":
    import sys
    if len(sys.argv) > 1:
        print(factorial(int(sys.argv[1])))
    else:
        for i in range(6):
            print(f"{i}! = {factorial(i)}")