Problem:
Score : 500 points

Problem Statement

There are N towns on a plane. The i-th town is located at the coordinates (x_i,y_i). There may be more than one town at the same coordinates.

You can build a road between two towns at coordinates (a,b) and (c,d) for a cost of min(|a-c|,|b-d|) yen (the currency of Japan). It is not possible to build other types of roads.

Your objective is to build roads so that it will be possible to travel between every pair of towns by traversing roads. At least how much money is necessary to achieve this?

Constraints

2 ≤ N ≤ 10^5

0 ≤ x_i,y_i ≤ 10^9

All input values are integers.

Input

Input is given from Standard Input in the following format:

N
x_1 y_1
x_2 y_2
:
x_N y_N

Output

Print the minimum necessary amount of money in order to build roads so that it will be possible to travel between every pair of towns by traversing roads.

Sample Input 1

3
1 5
3 9
7 8

Sample Output 1

3

Build a road between Towns 1 and 2, and another between Towns 2 and 3. The total cost is 2+1=3 yen.

Sample Input 2

6
8 3
4 9
12 19
18 1
13 5
7 6

Sample Output 2

8

Solution in Haskell (GHC 7.10.3) (judge verdict: Time Limit Exceeded)

import Data.List
import Data.Maybe
import Data.IntMap.Strict ((!))
import qualified Data.IntMap.Strict as M
import qualified Data.Set as S
import qualified Data.ByteString.Char8 as B

snub = S.toList . S.fromList
readInt = fst . fromJust . B.readInt
untilFix f x = if f x == x then x else untilFix f (f x)

kruskal n edge = makepath m0 0 edge
  where
    m0 = M.fromDistinctAscList (zip [1..n] [1..n])
    makepath _ acc [] = acc
    makepath forest acc (((a,b),d):abd)
      | rep1 /= rep2 = makepath forest1 (d+acc) abd
      | otherwise = makepath forest acc abd
      where
        v1 = min a b
        v2 = max a b
        rep1 = untilFix (forest!) v1
        rep2 = untilFix (forest!) v2
        forest1 = M.insert v2 rep1 (M.insert rep2 rep1 forest)

main = do
  getLine
  xys <- map ((\[x,y]->(x,y)) . map readInt . B.words) . B.lines <$> B.getContents
  let xyis = zip (snub xys) [1..]
  let xysx = sortOn fst xyis
  let xysy = sortOn (snd.fst) xyis
  print (built xysx xysy)

built xysx xysy = kruskal n edge
  where
    n = length xysx
    edge = sortOn snd (edgex ++ edgey)
    edgex = zipWith mkedge xysx (tail xysx)
    edgey = zipWith mkedge xysy (tail xysy)

mkedge ((xi,yi),i) ((xj,yj),j) = ((i,j), min (abs (xj-xi)) (abs (yj-yi)))