In classical mode you only have a limited amount of time to solve a puzzle and gain rating points.
Under the board you'll find a time bar with a marker running from right to left. The number on the left hand side shows you what your new rating will be if you fail the puzzle. In this case, 1338.
The number above the marker shows the rating you would obtain if you solved the puzzle correctly. This decreases constantly until it reaches your current rating. After that you won't gain any points even if you give the right solution, so you can only gain points if your time has not expired.