title: Convert binary string into integer
body: <p>I would like to convert a binary number writen in a String into its integer value. </p>
  
  <p>For example: </p>
  
  <pre><code>string input = "0101";
  int output = convert(input);
  </code></pre>
  
  <p><code>output</code> should be equal to <code>5</code> </p>