Suppose that a bank only permits passwords that are strings from the alphabet = {a, b, c, d, 1, 2, 3, 4} that follow the rules:

The length is at least five characters

It begins with a letter {a, b, c, d}

It ends with two digits {1, 2, 3, 4}

The set of legal passwords forms a regular language L. Construct a regular expression r such that L(r) = L.