using System;
using System.Collections.Generic;

public class Program
{
    private int N;
    private int[] X, Y;

    public void Solve()
    {
        var sc = new Scanner();
        N = sc.NextInt();
        X = new int[N];
        Y = new int[N];
        for (int i = 0; i < N; i++)
        {
            X[i] = sc.NextInt();
            Y[i] = sc.NextInt();
        }

        var xIndex = new int[N];
        var yIndex = new int[N];
        for (int i = 0; i < N; i++)
        {
            xIndex[i] = i;
            yIndex[i] = i;
        }

        Array.Sort(xIndex, (a, b) => X[a].CompareTo(X[b]));
        Array.Sort(yIndex, (a, b) => Y[a].CompareTo(Y[b]));

        var uf = new UnionFind(N);

        var edges = new List<Edge>();
        for (int i = 0; i < N - 1; i++)
        {
            edges.Add(new Edge(xIndex[i], xIndex[i + 1], X[xIndex[i+1]] - X[xIndex[i ]]));
            edges.Add(new Edge(yIndex[i], yIndex[i + 1], Y[yIndex[i+1]] - Y[yIndex[i ]]));
        }
        
        edges.Sort((a,b) => a.Dist.CompareTo(b.Dist));

        long ans = 0;

        foreach (Edge edge in edges)
        {
            if (!uf.Same(edge.X, edge.Y))
            {
                ans += edge.Dist;
                uf.Union(edge.X,edge.Y);
            }
        }
        Console.WriteLine(ans);
    }

    public static void Main(string[] args)
    {
        new Program().Solve();
    }
}

struct Edge
{
    public int X, Y, Dist;

    public Edge(int x, int y, int d)
    {
        X = x;
        Y = y;
        Dist = d;
    }
}

class UnionFind
{
    private int[] Par, Rank;

    public UnionFind(int max)
    {
        Par = new int[max];
        Rank = new int[max];
        for (int i = 0; i < max; i++)
        {
            Par[i] = i;
        }
    }

    private int Find(int n)
    {
        if (Par[n] == n)
        {
            return n;
        }
        else
        {
            return Find(Par[n]);
        }
    }

    public bool Same(int a, int b)
    {
        return Find(a) == Find(b);
    }

    public void Union(int a, int b)
    {
        a = Find(a);
        b = Find(b);
        if (a == b) return;
        if (Rank[a] < Rank[b])
        {
            Par[a] = b;
        }
        else
        {
            Par[b] = a;
            if (Rank[a] == Rank[b]) Rank[a]++;
        }
    }
}

class Scanner
{
    public Scanner()
    {
        _pos = 0;
        _line = new string[0];
    }

    const char Separator = ' ';
    private int _pos;
    private string[] _line;

    #region スペース区切りで取得

    public string Next()
    {
        if (_pos >= _line.Length)
        {
            _line = Console.ReadLine().Split(Separator);
            _pos = 0;
        }

        return _line[_pos++];
    }

    public int NextInt()
    {
        return int.Parse(Next());
    }

    public long NextLong()
    {
        return long.Parse(Next());
    }

    public double NextDouble()
    {
        return double.Parse(Next());
    }

    #endregion

    #region 型変換

    private int[] ToIntArray(string[] array)
    {
        var result = new int[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = int.Parse(array[i]);
        }

        return result;
    }

    private long[] ToLongArray(string[] array)
    {
        var result = new long[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = long.Parse(array[i]);
        }

        return result;
    }

    private double[] ToDoubleArray(string[] array)
    {
        var result = new double[array.Length];
        for (int i = 0; i < array.Length; i++)
        {
            result[i] = double.Parse(array[i]);
        }

        return result;
    }

    #endregion

    #region 配列取得

    public string[] Array()
    {
        if (_pos >= _line.Length)
            _line = Console.ReadLine().Split(Separator);

        _pos = _line.Length;
        return _line;
    }

    public int[] IntArray()
    {
        return ToIntArray(Array());
    }

    public long[] LongArray()
    {
        return ToLongArray(Array());
    }

    public double[] DoubleArray()
    {
        return ToDoubleArray(Array());
    }

    #endregion
}

Measured memory_bytes: 25380