<p>Given two integers <code>a</code> and <code>b</code>, return <strong>any</strong> string <code>s</code> such that:</p>
<ul>
<li><code>s</code> has length <code>a + b</code> and contains exactly <code>a</code><code>'a'</code> letters, and exactly <code>b</code><code>'b'</code> letters,</li>
<li>The substring <code>'aaa'</code> does not occur in <code>s</code>, and</li>
<li>The substring <code>'bbb'</code> does not occur in <code>s</code>.</li>