checking never ends.

no problems with small inputs. but it takes almost infinite time with large numbers, bigger than 100.

I believe I am trying quite ordinary soluution. Its basically equals to this code

def fib(n):
    if n==0 : return 0
    if n==1 : return 1
    return fib(n-1) + fib(n-2)

Is this normal so I should wait more, or do I have to find better algorithm?