2 entry "M" visa: how to calculate my deadline for last exit day

Hi,

Just got an “M”, “2” entries with a “60” day stay each time.
Issued “11oct2013” and enter before “11jan2014”.

I will arrive in Beijing the 5Nov2013, can you tell me which scenario is correct:

1.The deadline for my stay in mainland China is 11 jan2014 (i.e means I need to manage my spare exit/entry before this date)
2.The deadline for my stay in mainland China be determined from my second entry date + 60 days (i.e means that 11jan does not apply as last exit day)
Ex: I leave China the 4Jan2014 (4nov2013+60days), come back on 15Jan2014 and must leave by 15march2014 (60 days)