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'`.
- Each vowel `'u'` may only be followed by an `'a'.`

Since the answer may be too large, return it modulo `10^9 + 7.`

Example 1:

    Input: n = 1
    Output: 5
    Explanation: All possible strings are: "a", "e", "i" , "o" and "u".

Example 2:

    Input: n = 2
    Output: 10
    Explanation: All possible strings are: "ae", "ea", "ei", "ia", "ie", "io", "iu", "oi", "ou" and "ua".

Example 3:

    Input: n = 5
    Output: 68

Constraints:

- `1 <= n <= 2 * 10^4`