Implement a function “fizz_buzz(num)”, which return a string where:
- It returns "Fizz" if parameter(num) is divisible by 3.
- It returns "Buzz" if parameter(num) is divisible by 5.
- It returns "FizzBuzz" if parameter(num) is divisible by 3 and 5.
Return parameter(num as a string) if none of the above conditions are true.