# Can Convolution neutral network train(learn) separately (train different times)?

I am new in Convolution neutral network(CNN). My question is, is there a way to let CNN train separately? For example, at very beginning, CNN only need to learning hardwriting 0 and 1. After the training is good enough(0 and 1 only), now, I want CNN to learn hardwriting 2. So, since 0 and 1 had learned really good, is there a way to let CNN just learning hardwriting 2 only instead of learning everything (0 1 2) from scratch ??

You know, just like human brain, after you already know how to distinguish 0 and 1, we just need to learn 2, then we do can distinguish 0,1,2. instead of clean our memory first,then learning 0, 1,2 at same time. Because that efficiency is so low. Please advise me. Thanks.