title: Regex to match first number only if the string starts with 3 numbers in a row
body: <p>I have to make a regex which selects the first number only if there are 3 numbers in a row in the beginning of the string.</p>
  
  <p>Example:</p>
  
  <pre><code>012 test
  </code></pre>
  
  <p>Here I'd like to match the 0 at the beginning of the string.</p>
  
  <pre><code>02 test
  </code></pre>
  
  <p>Here I want nothing to be matched by the regex.</p>
  
  <p>I have no idea how to check the string without matching it using regex. Is this possible?</p>