Total Number of Unique Characters

Given two strings, create a function that returns the total number of unique characters from the combined string.

Examples

count_unique("apple", "play") ➞ 5
# "appleplay" has 5 unique characters:
# "a", "e", "l", "p", "y"

count_unique("sore", "zebra") ➞ 7

count_unique("a", "soup") ➞ 5

Notes

• Each word will contain at least one letter.
• All words will be lower cased.