input: Write a function to generate a random number between the given input numbers. The function should return the random number.
  assert random_num(0, 10)== random_num(0, 10)
  assert random_num(20, 30)== random_num(20, 30)
  assert random_num(-10, 10)== random_num(-10, 10)
  assert random_num(50, 70)== random_num(50, 70)
  assert random_num(-50, -30)== random_num(-50, -30)
output: import random
  
  def random_num(a, b):
      return random.randint(a, b)