1220. Count Vowels Permutation

Given an integer n, your task is to count how many strings of length n can be formed under the following rules: - Each character is a lower case vowel ('a', 'e', 'i', 'o', 'u') - Each vowel 'a' may only be followed by an 'e'. - Each vowel 'e' may only be followed by an 'a' or an 'i'. - Each vowel 'i' may not be followed by another 'i'. - Each vowel 'o' may only be followed by an 'i' or a 'u'.