hey, i am having a little bit of trouble when i call calc....for example, if i do this:

//echo -a $calc(5599395841418 - 500)

it echos this:
5599395840917.999616

when it should just return:

5599395840918

500 less then what it was, why am i getting 501 less then what it was, PLUS a dot and more numbers after it :|

i dont need the dot, and whatever is after it, all thats doing it causing problems for what i'm doing, any ideas?