S2 type will expire 04/ 9/15. I entered China 03/17/15 Can I stay for 30 days even my visa expires?

I have S2 type (Multiple) I arrived China March 17, 2015. My S2 type is going to expire April 09, 2015. Do I need to exit on April 9, 2015 or I can stay 30 days in China till April 16, 2015? (as what is stated there that 30 days stay upon entry).

Thank you very much