input: Write a function to generate a random string of specified length using only lowercase letters. The function should take an integer as input and return a string.
  import random
  import string
  
  def random_string(length):
      letters = string.ascii_lowercase
      return ''.join(random.choice(letters) for i in range(length))
  
  random_string(6)
output: import random
  import string
  
  def random_string(length):
      letters = string.ascii_lowercase
      return ''.join(random.choice(letters) for i in range(length))