Tracking Devices

Farmer Ran has created a state-of-the-art farm. To keep up with the
newest technogolies, he decided to equip all his cows with radio
tracking devices so he knows at all times where on the farm each cow
is.

To determine the location of his cows, he is going to install N (1 <=
N <= 250) identical receivers on his farm so that every location on
the farm can communicate with at least one radio. The farm is a
rectangle with coordinates (0,0) to (FX,FY) (both FX and FY are in
the range 1..1,000,000). FR wants to determine the range required for
the radios so that every location on the farm is reachable.  Since
receivers with larger ranges are more expensive, he wants to minimize
this range. How big a range does he need?

PROBLEM NAME: track

INPUT FORMAT:

* Line 1: Two space-separated integers: FX and FY

* Line 2: The integer N

* Lines 3..N+2: Each line contains two space-separated integers, Xi
        and Yi, the coordinates of the i'th receiver (0 <= Xi <= FX
        and 0<= Yi <= FY).

SAMPLE INPUT:

3 2
4
0 1
1 1
3 0
3 2

OUTPUT FORMAT:

* Line 1: A single line with one real number, the minimal range,
        rounded off to the nearest two decimal places.

SAMPLE OUTPUT:

1.25

OUTPUT DETAILS:

The point (1.75,0) for example has distance 1.25 to the receiver at (3,0).