Integer to English Words

You are given a non-negative integer num. Your task is to express this number using correct English words.

The representation should follow standard English wording rules:

• Use words like “Thousand”, “Million”, “Billion” when appropriate.

• Numbers below 20 have unique names.

• Tens such as 20, 30, 40 … 90 follow a structured format.

• Zero must be written as "Zero".

Return a string that spells out the value of num in clear English wording.