(http://en.wikipedia.org/wiki/Fibonacci_number)

Write a program that generates the nth number in a fibonacci sequence (starting at 0). The program should start and ask two things:

The number that will describe the nth term you want to get if the function should be recursive or not The program should count with data validation. It means that the program must inform the user when the number she inserted is invalid.

Extra: If the user passes a --recursive argument, the program should not ask for the function to use and use the recursive function.