# Fibonacci numbers done recursively
# ECS 10, May 26, 2009
# Matt Bishop

# function to compute fib(n)
# parameter: n, a non-negative integer
# returns: n-th Fibonacci number
def fib(n):
    # base case: n = 0
    if n == 0 or n == 1:
        return 1
    # recursion here
    else:
        return fib(n-1) + fib(n-2)

# wrapper for fib(n); check inputs
# parameter: n, a non-negative integer
# returns: nth Fibonacci number on success, -1 on error
# calls: fib(n): computes nth Fibonacci number
def fullfib(n):
    # quick check for numeric type
    try:
        n += 0
    except TypeError:
        return -1
    # check to be sure it's non-negative
    if n < 0:
        return -1
    # now check that it is an int
    if n != int(n):
        return -1
    # it's okay
    return fib(n)