Given an integer `n`, return the number of strings of length `n` that consist only of vowels (`a`, `e`, `i`, `o`, `u`) and are lexicographically sorted.

A string `s` is lexicographically sorted if for all valid `i`, `s[i]` is the same as or comes before `s[i+1]` in the alphabet.

Example 1:

    Input: n = 1
    Output: 5
    Explanation: The 5 sorted strings that consist of vowels only are ["a","e","i","o","u"].

Example 2:

    Input: n = 2
    Output: 15
    Explanation: The 15 sorted strings that consist of vowels only are
    ["aa","ae","ai","ao","au","ee","ei","eo","eu","ii","io","iu","oo","ou","uu"].
    Note that "ea" is not a valid string since 'e' comes after 'a' in the alphabet.

Example 3:

    Input: n = 33
    Output: 66045

Constraints:

- `1 <= n <= 50`