title: LINQ to find the closest number that is greater / less than an input
body: <p>Suppose I have this number list:</p>
  
  <pre><code>List&lt;int&gt; = new List&lt;int&gt;(){3,5,8,11,12,13,14,21}
  </code></pre>
  
  <p>Suppose that I want to get the closest number that is less than 11, it would be 8
  Suppose that I want to get the closest number that is greater than 13 that would be 14.</p>
  
  <p>The numbers in list can't be duplicated and are always ordered. How can I write Linq for this?</p>