input: 
  def largest_prime_factor(n):
      """
      Find the largest prime factor of the given number n.
      >>> largest_prime_factor(331)
      331
      """
  
output:     if n <= 1:
          return None
      largest_factor = 1
      for i in range(2, int(n**0.5) + 1):
          while n % i == 0:
              largest_factor = i
              n //= i
      if n > 1:
          largest_factor = n
      return largest_factor