title: Regular Expression Problem - Matching A Single Letter. Exclude consecutive letters
body: <p>I'm having an issue creating a regular expression that will give me what I want. I need your help! So the text we are using is:</p>
  
  <pre><code>S      1SS          1S
  </code></pre>
  
  <p>"S" and "1S" are matches. "1SS" is not a match. I would like it to be a little more specific than just excluding anything with three characters but that may be a solution.</p>
  
  <p>Any other ideas on how to exclude "1SS"? I can't figure it out!</p>
  
  <p>Thank you,</p>
  
  <p>Mark S.</p>