#!/usr/bin/env python
 
def fib(n):
  '''
  Simple script to test out recursive function in python. This function returns 
  the Fibonacci number for the given argument. 

  Copyright Yves Dorfsman 2008.

  This is free software ; You can redistribute it and/or modify it under the
  terms of the GNU General Public License as published by the Free Software
  Foundation; either version 2 of the License, or (at your option) any
  later version.
  '''
 
  # validate that we don't get a non-numerical string etc...
  try:
    n = int(n)
  except:
    raise
 
  if n < 0:
    raise ValueError
 
  elif n == 0:
    p = 0
 
  elif n == 1:
    p = 1
 
  else:
    l = fib(n-1)
    m = fib(n-2)
    p = l + m
 
  return p
 
 
 

import sys
 
if __name__ == '__main__':
  if len(sys.argv) >= 2:
 
    f = fib(sys.argv[1])
    print f
 
  else:
    raise ValueError