The challenge is to take any real number as input and output or return the absolute value. You may not use any built-in functions other than those dealing with input and output/returning. This is code golf, so the shortest code wins. This is my first question here, so bear with me if I've left something obvious out of the challenge.
As per Quincunx's suggestion, I am limiting input to anywhere between -9E99 and 9E99.
Also, the only functions/operators you can use are
square root or their equivalents