input: Write a function to generate a random number between the given input numbers.
  assert random_num(2, 15) in range(2, 16)
  assert random_num(10, 50) in range(10, 51)
  assert random_num(-5, 5) in range(-5, 6)
  assert random_num(0, 0) == 0
  assert random_num(1, 1) == 1
output: import random
  
  def random_num(a, b):
      return random.randint(a, b)