Building the Moat

To repel invading thirsty aardvarks, Farmer Ran (FR) wants to build a moat
around his farm. He owns N (3 <= N <= 50,000) watering holes, and will be
digging the moat in a straight line between pairs of them. His moat should
protect (i.e., surround) all his watering holes; every watering hole must
be on or inside the moat, and the moat must form a closed loop.

Digging a moat is expensive work, and FR wants his moat to have the
minimum length possible. Find the length of the shortest moat he can construct.

The unique holes are each located at integer coordinates in the range
-20,000..20,000.

Consider this grid where the 20 '*'s represent watering holes:

...*-----------------*......
../..........*........\.....
./.....................\....
*......................*\...
|..........*........*....\..
|*........................\.
|..........................*
*..........................|
.\*........................|
..\.....................*..|
...\........*............*.|
....\..................*...*
.....\..*..........*....../.
......\................../..
.......*----------------*...

The enclosing lines are the shortest possible path that can enclose this
set of watering holes.

The line displacements, starting with the top line are: (18,0), (6,-6),
(0,-5), (-3,-3), (-17,0), (-7,7), (0,4), and (3,3).  This yields a distance
of 70.8700576850888(...).

PROBLEM NAME: moat

INPUT FORMAT:

* Line 1: A single integer, N.

* Lines 2..N+1: Two space-separated integers, X_i and Y_i that specify
        the location of a watering hole.

SAMPLE INPUT:

20
2 10
3 7
22 15
12 11
20 3
28 9
1 12
9 3
14 14
25 6
8 1
25 1
28 4
24 12
4 15
13 5
26 5
21 11
24 4
1 8

OUTPUT FORMAT:

* Line 1: A single number D, the shortest possible length of moat.
        Print this number, rounded to two places of precision to the
        right of the decimal point.

SAMPLE OUTPUT:

70.87