input: Write a python function to convert letters to their corresponding numbers using the given dictionaries and vice versa.
  assert convert('a') == 1
  assert convert(1) == 'a'
  assert convert('z') == 26
  assert convert(26) == 'z'
  assert convert('m') == 13
  assert convert(13) == 'm'
output: def convert(value):
      letter_to_number = {chr(i + 96): i for i in range(1, 27)}
      number_to_letter = {i: chr(i + 96) for i in range(1, 27)}
      
      if isinstance(value, str):
          return letter_to_number[value]
      elif isinstance(value, int):
          return number_to_letter[value]