Roll your own 64bit integer. It's pretty much like 32bit arithmetic, except that you need to take care of the carry yourself. Gives you access to 1.8446744074×10^19 numbers.

An alternative would be double (don't use float), the largest integer you can represent without running into rounding errors is 2^53+1.

long long int and the likes doesn't exist in Lite-C, neither does the concept of an unsigned variable. 32 bit integers is all you get before you have to look into alternatives.