Help on an Excel formula

I need some help on an Excel formula..

I need to calculate a formula to count the exact number of days between two dates.

For Example:

Cell A1 contains 01/01/2007
Cell A2 contains 31/01/2007
Cell A3 needs to contain the answer (31)
All the formula’s i can think of return the answer (30).

I would very much appreciate your help on this one.