input: Write a function to implement the FizzBuzz logic.
  assert fizzbuzz(15) == 'FizzBuzz'
  assert fizzbuzz(9) == 'Fizz'
  assert fizzbuzz(10) == 'Buzz'
  assert fizzbuzz(7) == 7
output: def fizzbuzz(n):
      if n % 3 == 0 and n % 5 == 0:
          return 'FizzBuzz'
      elif n % 3 == 0:
          return 'Fizz'
      elif n % 5 == 0:
          return 'Buzz'
      else:
          return n