title: Check the least number of colors needed to color graph (chromatic number in 2-regular graph)
body: <p>My task is to check the least number of colors used in graph coloring which is simply chromatic number of graph. My undirected graph is 2-regular (each vertex is 2-degree). I found solution that</p>
  
  <p><em>(maximum independent set number)/number of vertices = number of colors
  (chromatic number)</em></p>
  
  <p><a href="https://imgur.com/a/ZtyP4v9" rel="nofollow noreferrer">https://imgur.com/a/ZtyP4v9</a>  - how it looks like</p>
  
  <p>As you see, it can be 2-colored if result is 2 or 3-colored if the result is more than 2.</p>
  
  <p>But I have no idea how I could find an maximum independent set in such graph.</p>