How do I find the last element in an HTML File with PHP Simple HTML DOM Parser?

According to the documentation for SIMPLE HTML DOM PARSER (under the tab “How to modify HTML Elements”), this code finds the first instance of <div class="hello">:

$html = str_get_html('<div class="hello">Hello</div><div class="world">World</div>');

$html->find('div[class=hello]', 0)->innertext = 'foo';

echo $html; // Output: <div class="hello">foo</div><div class="world">World</div>

What if I want to insert 'foo' into the last instance of <div class="hello">, assuming that the HTML code has a lot of instances of <div class="hello">.

What should replace the 0?