SNMP Monitoring Memory on 1720

Hi folks,

I have a 1720 with IOS 12.4. It has 48MB of RAM and 16MB of flash. I'm trying to find out using snmp how much memory is used, free etc. I think I found the correct one and to verify this I ran the command "sh memory statistics". but this displays the following...

Head Total(b) Used(b) Free(b) Lowest(b) Largest(b)

Processor 81834C1C 19509760 6232520 13277240 13148716

I/O 2A8B400 5721088 1551656 4169432 4164448 416940

Can someone please tell me how this relates to the 48MB of ram?

Or is there a simpler oid I can use to get free memory and used in total, not divided by processor and i/o?

thanks Dave