ROSALIND FIB

Given: Positive integers n≤40 and k≤5.
Return: The total number of rabbit pairs that will be present after n
months, if we begin with 1 pair and in each generation, every pair of reproduction-age rabbits produces a litter of k rabbit pairs (instead of only 1 pair).

import sys

def F(n, k):
 Fn_2 = 1
 Fn_1 = k+1
 if n > 1:
  i = 3
  while i < n:
   Fn = Fn_1 + k*Fn_2
   Fn_2 = Fn_1
   Fn_1 = Fn
   i+=1
  return Fn
 elif n == 1:
  return 1
 elif n == 2:
  return k+1

def main():
 if len(sys.argv) > 1:
  print F(int(sys.argv[1]), int(sys.argv[2]))
 else:
  print 'Enter k and n.'

if __name__ == '__main__':
 main()