Write a function that returns the index of the first occurrence of the word "Wally". "Wally" must not be part of another word, but it can be directly followed by a punctuation mark. If no such "Wally" exists, return -1.
Examples:
"Wally" => 0
"Where's Wally" => 8
"Where's Waldo" => -1
"DWally Wallyd .Wally" => -1
"Hi Wally." => 3
"It's Wally's." => 5
"Wally Wally" => 0
"'Wally Wally" => 7