In my past few contests, including the most recent one, I have noticed that I keep getting stuck on easy problems which prevents me from being able to devote more time to solving harder ones. For instance, in the last contest, after solving A in 3min, it took me another half hour before I could solve B. However, I was able to solve C only 12min thereafter — which indicates that the cause of my taking too long on B was probably not a lack of skill but is rather due to something else. What strategy should I use to overcome this?