You are given *N* non-overlapping circles in xy-plane. The radius of each circle varies, but the radius of
the largest circle is not double longer than that of the smallest.

Figure 1: The Sample Input

The distance between two circles *C*_{1} and *C*_{2} is given by the usual formula

where (*x _{i}*,

Your task is to write a program that finds the closest pair of circles and print their distance.

The input consists of a series of test cases, followed by a single line only containing a single zero, which indicates the end of input.

Each test case begins with a line containing an integer *N* (2 ≤ *N* ≤ 100000), which indicates the number
of circles in the test case. *N* lines describing the circles follow. Each of the *N* lines has three decimal
numbers *R*, *X*, and *Y*. R represents the radius of the circle. *X* and *Y* represent the *x*- and *y*-coordinates of
the center of the circle, respectively.

For each test case, print the distance between the closest circles. You may print any number of digits after the decimal point, but the error must not exceed 0.00001.

4 1.0 0.0 0.0 1.5 0.0 3.0 2.0 4.0 0.0 1.0 3.0 4.0 0

0.5

Source: ACM-ICPC Japan Alumni Group Summer Camp 2006
, Day 1, Tokyo, Japan, 2006-09-22

http://acm-icpc.aitea.net/

http://acm-icpc.aitea.net/