using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using static System.Math;
using static System.Array;
using static AtCoder.Tool;
namespace AtCoder
{
    class AC
    {
        const int MOD = 1000000007;
        const int INF = int.MaxValue / 2;
        const long SINF = long.MaxValue / 2;
        const double EPS = 1e-8;
        static readonly int[] dx = { 0, 1, 0, -1 };
        static readonly int[] dy = { 1, 0, -1, 0 };
        //static List<List<int>> G = new List<List<int>>();
        //static List<List<Edge>>G = new List<List<Edge>>();
        //static List<Edge> E = new List<Edge>();


        static void Main(string[] args)
        {
            //var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            //Console.SetOut(sw);
            var cin = new Scanner();

            int N = int.Parse(Console.ReadLine());
            var P = new List<Tuple<int, int, int>>();
            for(var i = 0; i < N; i++)
            {
                var input = cin.SplitRead();
                P.Add(new Tuple<int, int, int>(input[0], input[1], i));
            }
            var ed = new List<Tuple<int, int, int>>();//dist,ind i ,ind j
            P.Sort((x, y) => (x.Item1 - y.Item1));
            for(var i = 1; i < N; i++)
            {
                ed.Add(new Tuple<int, int, int>(Abs(P[i].Item1 - P[i - 1].Item1), P[i].Item3, P[i - 1].Item3));
            }
            P.Sort((x, y) => (x.Item2 - y.Item2));
            for(var i = 1; i < N; i++)
            {
                ed.Add(new Tuple<int, int, int>(Abs(P[i].Item2 - P[i - 1].Item2), P[i].Item3, P[i - 1].Item3));
            }

            long ans = 0;
            var uf = new UnionFind(N);

            ed.Sort((x, y) => (x.Item1 - y.Item1));
            foreach(var e in ed)
            {
                int dis = e.Item1;
                int i = e.Item2;
                int j = e.Item3;

                if (uf.SameRoot(i, j)) { continue; }
                ans += dis;
                uf.Unite(i, j);
            }

            Console.WriteLine(ans);



            //Console.Out.Flush();
        }
        public class UnionFind
        {
            public int[] parent;
            public int[] rank;
            public int[] size;
            public UnionFind(int n)
            {
                parent = new int[n];
                rank = new int[n];
                size = new int[n];
                for (var i = 0; i < n; i++)
                {
                    parent[i] = i;
                    rank[i] = 0;
                    size[i] = 1;
                }
            }

            private int Root(int x)
            {
                return parent[x] == x ? x : parent[x] = Root(parent[x]);
            }

            public bool SameRoot(int x, int y)
            {
                return Root(x) == Root(y);
            }

            public void Unite(int x, int y)
            {
                x = Root(x);
                y = Root(y);
                if (x == y) { return; }

                if (rank[x] < rank[y])
                {
                    parent[x] = y;
                    size[y] += size[x];
                    size[x] = 0;
                }
                else
                {
                    parent[y] = x;
                    if (rank[x] == rank[y]) { rank[x]++; }
                    size[x] += size[y];
                    size[y] = 0;
                }
            }

            public int GetSize(int x)
            {
                return size[Root(x)];
            }

        }
        struct Edge
        {
            public int from;

            public int to;
            public long dist;
            public Edge(int t, long c)
            {
                from = -1;
                to = t;
                dist = c;
            }
            public Edge(int f, int t, long c)
            {
                from = f;
                to = t;
                dist = c;
            }

        }
        struct Pair<T, U> : IComparable<Pair<T, U>>
        where T : IComparable<T>
        where U : IComparable<U>
        {
            public T first;
            public U second;
            private readonly bool CompWithFirst;

            public Pair(T f, U s, int comp)
            {
                first = f;
                second = s;
                CompWithFirst = comp == 1;
            }
            public Pair(T f, U s)
            {
                first = f;
                second = s;
                CompWithFirst = true;
            }

            public int CompareTo(Pair<T, U> other)
            {
                return CompWithFirst ? first.CompareTo(other.first) : second.CompareTo(other.second);
            }
        }
    }
   
    public class PriorityQueue<T> where T : IComparable<T>
    {

        private List<T> Q;
        private readonly int r;

        public PriorityQueue(bool ascending)
        {
            if (ascending)
            {
                r = 1;
            }
            else
            {
                r = -1;
            }
            Q = new List<T>();
        }


        private void PushHeap(List<T> list, T item)
        {
            int n = list.Count();
            list.Add(item);

            while (n != 0)
            {
                int pIndex = (n - 1) / 2;

                if (list[n].CompareTo(list[pIndex]) * r > 0)
                {
                    Swap(Q, n, pIndex);
                }
                else { break; }

                n = pIndex;
            }
        }

        private void PopHeap(List<T> list)
        {
            int n = list.Count() - 1;
            list[0] = list[n];
            list.RemoveAt(n);

            int cur = 0;
            int comp;

            while (2 * cur + 1 <= n - 1)
            {
                int c1 = 2 * cur + 1;
                int c2 = 2 * (cur + 1);
                if (c1 == n - 1)
                {
                    comp = c1;
                }
                else
                {

                    comp = list[c1].CompareTo(list[c2]) * r > 0 ? c1 : c2;
                }

                if (list[cur].CompareTo(list[comp]) * r < 0)
                {
                    Swap(Q, cur, comp);
                }
                else { break; }

                cur = comp;
            }
        }

        private void Swap(List<T> list, int a, int b)
        {
            T keep = list[a];
            list[a] = list[b];
            list[b] = keep;
        }



        public void Enqueue(T value)
        {
            PushHeap(Q, value);
        }

        public T Dequeue()
        {
            T ret = Q[0];
            PopHeap(Q);
            return ret;
        }

        public T Peek()
        {
            return Q[0];
        }

        public int Count()
        {
            return Q.Count();
        }

        public bool Contains(T search)
        {
            return Q.Contains(search);
        }
    }
    public class Scanner
    {
        public int[] SplitRead()
        {
            int[] array = Console.ReadLine().Split().Select(int.Parse).ToArray();
            return array;
        }
        public long[] SplitReadL()
        {
            long[] array = Console.ReadLine().Split().Select(long.Parse).ToArray();
            return array;
        }
    }
    public static class Tool
    {
        static public void Initialize<T>(ref T[] array, T initialvalue)
        {
            for (var i = 0; i < array.Length; i++)
            {
                array[i] = initialvalue;
            }
        }
        static public void Swap<T>(T[] a, int i, int j)
        {
            T k = a[i];
            a[i] = a[j];
            a[j] = k;
        }

    }

}


Measured memory_bytes: 35504