input: Write a function to determine the number of bits required to represent a given number.
  assert bits_required(0) == 1
  assert bits_required(1) == 1
  assert bits_required(2) == 2
  assert bits_required(3) == 2
  assert bits_required(255) == 8
  assert bits_required(256) == 9
output: def bits_required(n):
      return len(bin(n)[2:]) if n != 0 else 1