Dealing With Negative Numbers In Nested If

I don't know how to manipulate the formula with quoting the "You can't have cups less than zero".

Teletubbies coffee - Nested If

Create a nested If function to describe the Teletubbies coffee drinking habits based on the following criteria:

0 cups = Tea drinker

1-5 cups = Normal

More than 5 cups = Caffeine fiend

Copy the function down and check that it works.

How to structure the If function

Try modifying the If function so that if Cups of coffee is a negative number you see an appropriate error message. Make sure the rest of the function still works!