Programming a calulator

How can I hack this cheap solar-powered calculator that the bank gave me for Christmas? It has, like, four bytes of memory and can display seven numbers on the screen. It has no interface at all, so I'll probably have to dust off the old soldering iron and put a serial bus in. Ideas on where to begin?

It's not like you can do anything useful with it. Use it for its original purpose.

>>2
You are locked in a large room with a large quantity of food and water. You have a large number of 74xx ICs (as well as their datasheets) and a few calculators like the one described in >>1. The exit door is locked with a password. The password is the sum of the first 1000 prime number.

>>3
Sounds exactly like every single morning of my life.

>>3
I'll drink my own cum and eat my own shit.

>>3
I'll stay in the room forever. Having a large quantity of food and water is quite a good situation to be in indeed after the collapse.

>>6
Okay, how about this. You are locked in a large room with a virtually unlimited quantity of food and water. You have a large number of 74xx ICs (as well as their datasheets) and a few calculators like the one described in >>1. Located under the room is a large bomb set to explode in one year unless you enter the sum of the first 10000 prime numbers on a keypad.

>>7
496165411 won't fit in a 7-digit calculator.

>>8
Use two or more.

I don't know the first damned thing about electronics.

>>1
DO NOT TRUST THIS JEW CALCULATOR!  It will skew your calculations in favor of the bank.  So you better pogrom it out of the window before it corrupts you, or better into a fire.