ROSALIND FIBD

Given: Positive integers n≤100 and m≤20.
Return: The total number of pairs of rabbits that will remain after the n
-th month if all rabbits live for m months.

import sys

def F(n, m):
 if n < 2:
  return 1
 else:
  Old = [0, 0, 1]
  New = [0, 1, 0]
  month = 3
  while month <= n:
   born_to_die = month - m - 1
   if born_to_die < 0:
    Died = 0
   else:
    Died = New[born_to_die]
   Old_add = Old[month - 1] + New[month - 1] - Died
   New_add = Old[month - 1] - Died
   Old.append(Old_add)
   New.append(New_add)
   month+=1
  return Old[n] + New[n] - New[n - m]

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

if __name__ == '__main__':
 main()