Given an integer n, return the number of valid strings of length n that can be formed using lowercase vowels ('a', 'e', 'i', 'o', 'u') according to the following rules:

• 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 very large, return it modulo $10^9 + 7$.

Constraints:

• $1 \le n \le 2 \cdot 10^4$

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