input: Write a python function to find the maximum number of vowels that can follow after the given consonants.
  assert max_vowels(['b', 'c', 'd', 'f']) == 4
  assert max_vowels(['g', 'h', 'j', 'k', 'l']) == 5
  assert max_vowels(['p', 'q', 'r', 's', 't', 'v']) == 6
output: def max_vowels(consonants):
      vowels = 'aeiou'
      return len(consonants) * len(vowels)