Underground Cables

A city wants to get rid of its unsightly power poles by moving all of its power cables underground. It has a list of points that all need to be connected, but there are some limitations. The tunneling equipment can only move in straight lines between points, and there is room for only one underground cable at any location other than the given points, so no two cables may cross.

Given the list of points, what is the least total length of cable needed so that every pair of points is connected, either directly or indirectly through other points?

The input consists of several test cases. Each test case begins with an integer $N$ ($2 \le N \le 1000$), the number of points in the city. Each of the next $N$ lines contains two integers $X$ and $Y$ ($-1000 \le X, Y \le 1000$), the $(X, Y)$ location of a point.

The input ends with a line containing a single $0$.

For each test case, output on its own line a single real number: the least total length of cable needed to connect all of the points. Print this value rounded to two decimal places.