First N Vowels

Write a function that returns the first n vowels of a string.

Examples

first_n_vowels("sharpening skills", 3) ➞ "aei"

first_n_vowels("major league", 5) ➞ "aoeau"

first_n_vowels("hostess", 5) ➞ "invalid"

Notes

• Return "invalid" if the n exceeds the number of vowels in a string.
• Vowels are: a, e, i, o, u