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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Linq;
using System.IO;
using System.Text;
using System.Collections;
using System.Collections.Generic;
using System.Text.RegularExpressions;

namespace AtCoder.ABC065
{
    class Program
    {
        static int[] parent;
        static void Main()
        {
            int n = int.Parse(Console.ReadLine());
            int[] x = new int[n];
            int[] y = new int[n];
            for (int i = 0; i < n; i++)
            {
                string[] inputs = Console.ReadLine().Split(' ');
                x[i] = int.Parse(inputs[0]);
                y[i] = int.Parse(inputs[1]);
            }
            var sortedX = x.Select((elem, idx) => new { Value = elem, Index = idx })
                            .OrderBy(elem => elem.Value)
                            .ToArray();
            var sortedY = y.Select((elem, idx) => new { Value = elem, Index = idx })
                            .OrderBy(elem => elem.Value)
                            .ToArray();
            Edge[] edges = new Edge[2 * (n - 1)];
            int k = 0;
            for (int i = 1; i < n; i++)
            {
                edges[k++] = new Edge(sortedX[i - 1].Index, sortedX[i].Index, sortedX[i].Value - sortedX[i - 1].Value);
                edges[k++] = new Edge(sortedY[i - 1].Index, sortedY[i].Index, sortedY[i].Value - sortedY[i - 1].Value);
            }
            // Console.Error.WriteLine(edges.Length);
            // foreach (Edge elem in edges) Console.Error.WriteLine(elem.Cost);
            Array.Sort(edges);
            parent = Enumerable.Range(0, n).ToArray();
            long totalCost = 0;
            for (int i = 0; i < k; i++)
            {
                if (Root(edges[i].NodeId1) != Root(edges[i].NodeId2))
                {
                    totalCost += edges[i].Cost;
                    Console.Error.WriteLine("{0}:{1} - {2}:{3}", parent[edges[i].NodeId1], edges[i].NodeId1, parent[edges[i].NodeId2], edges[i].NodeId2);
                    int theirRoot = Math.Min(Root(edges[i].NodeId1), Root(edges[i].NodeId2));
                    parent[edges[i].NodeId1] = theirRoot;
                    parent[edges[i].NodeId2] = theirRoot;
                    Console.Error.WriteLine("total cost = {0} <- {1}", totalCost, edges[i].Cost);
                }
            }
            Console.WriteLine(totalCost);
        }

        static int Root(int id)
        {
            return parent[id] == id ? id : parent[id] = Root(parent[id]);
        }
    }

    class Edge : IComparable
    {
        public int NodeId1 { get; }
        public int NodeId2 { get; }
        public long Cost { get; }
        public Edge(int id1, int id2, long cost)
        {
            NodeId1 = id1;
            NodeId2 = id2;
            Cost = cost;
        }
        public int CompareTo(Object obj)
        {
            return this.Cost.CompareTo(((Edge)obj).Cost);
        }
    }
}