Hello S deshmukh,

I would personally suggest you to go for books instead of the smartphones app or online website as nothing can beat book.

As in case of smartphone you will waste a lot of your time in checking post,notification or messages knowingly or unknowingly. 

If you want a website still then i would suggest you to go for toppr.com as site have it's own app with same name on play store. 

Hope it helps.

Thank you :)