// Original C++ solution (slower):
#include <iostream>

#include <vector>

#include <algorithm>

#include <cstdlib>

#include <queue>



using namespace std;



struct Point

{

	int x, y, i;

};



bool cmpX(Point& p1, Point& p2)

{

    return p1.x < p2.x;

}



bool cmpY(Point& p1, Point& p2)

{

	return p1.y < p2.y;

}



vector<int> visited;

vector<Point> points, points2;

vector< vector< pair<int, int> > > graph;

priority_queue< pair<int, int>, vector< pair<int, int> >, greater< pair<int, int> > > pq;



int main()

{

    int N;

    cin >> N;

	points.resize(N);

	visited.assign(N, 0);

	graph.resize(N);

    for (int i = 0; i < N; ++i) {

        cin >> points[i].x >> points[i].y;

        points[i].i = i;

    }



    points2 = points;

    sort(points2.begin(), points2.end(), cmpX);

    for (int i = 1; i < points2.size(); ++i) {

		int dist = points2[i].x - points2[i-1].x;

		graph[ points2[i].i ].push_back(make_pair(dist, points2[i-1].i));

		graph[ points2[i-1].i ].push_back(make_pair(dist, points2[i].i));

    }



    points2 = points;

    sort(points2.begin(), points2.end(), cmpY);

    for (int i = 1; i < points2.size(); ++i) {

		int dist = points2[i].y - points2[i-1].y;

		graph[ points2[i].i ].push_back(make_pair(dist, points2[i-1].i));

		graph[ points2[i-1].i ].push_back(make_pair(dist, points2[i].i));

    }



    long long ans = 0;

    pq.push(make_pair(0, 0));

    while (!pq.empty()) {

        pair<int, int> edge = pq.top();

//        cout << edge.first << ' ' << edge.second << endl;

        pq.pop();





		int u = edge.second;

		if (visited[u]) continue;

		visited[u] = 1;

        ans += edge.first;





		for (int i = 0; i < graph[u].size(); ++i) {

			pair<int, int> p = graph[u][i];

            pq.push(p);

		}

    }



    cout << ans << endl;

}


// Optimized solution to the same problem (faster):
#include <stdio.h>

#include <stdlib.h>

#include <algorithm>



// 全局变量

const int N = 100010 , M = N + N;

int x[N],y[N],id[N],n;



typedef struct ufset *UFset;

struct ufset

{

  int *parent;

  int *root;

};

UFset UFinit(int size)

{

  int e;

  UFset U=(UFset)malloc(sizeof *U);

  U->parent=(int*)malloc((size+1)*sizeof(int));

  U->root=(int*)malloc((size+1)*sizeof(int));

  for(e=1; e<=size; e++)

  {

    U->parent[e]=1;

    U->root[e]=1;

  }

  return U;

}

int UFfind(int e,UFset U)

{

  int i,j = e;

  while(!U->root[j]) j = U->parent[j];

  while(j!=e){

    i = U->parent[e];

    U->parent[e]=j;

    e=i;

  }

  return j;

}

int UFunion(int i,int j,UFset U)

{

  if(U->parent[i]<U->parent[j])

  {

    U->parent[j]+=U->parent[i];

    U->root[i]=0;

    U->parent[i]=j;

    return j;

  }

  else

  {

    U->parent[i]+=U->parent[j];

    U->root[j]=0;

    U->parent[j]=i;

    return i;

  }

}



// 记录优化后的边集数

struct Edge

{

  int u, v, cost;

  bool operator <(const Edge&b) const

  {

    return cost < b.cost;

  }

} edge[M];

int tot;

// 按照X轴排序

bool cmpX(int a, int b)

{

  return x[a] < x[b];

}

// 按照Y轴排序

bool cmpY(int a, int b)

{

  return y[a] < y[b];

}

void add(int c, int a, int b)

{

  edge[tot].cost = c;

  edge[tot].u = a;

  edge[tot++].v = b;

}

int main()

{

  scanf("%d", &n);

  int i;

  for (i = 1; i <= n; ++i)

  {

    scanf("%d%d", x + i, y + i);

    id[i] = i;

  }

  std::sort(id + 1 , id + n + 1, cmpX);

  for (i = 2; i <= n; ++i)

    add(x[id[i]] - x[id[i - 1]], id[i], id[i - 1]);

  std::sort(id + 1 , id + n + 1, cmpY);

  for (i = 2; i <= n; ++i)

    add(y[id[i]] - y[id[i - 1]], id[i], id[i - 1]);

  UFset UFS = UFinit(n);



  // 按照花费排序

  std::sort(edge, edge + tot);

  long long totcost = 0;

  for (i = 0; i < tot; ++i)

  {

    int u = edge[i].u, v = edge[i].v;

    u = UFfind(u,UFS), v = UFfind(v,UFS);

    if (u != v)

    {

      UFunion(u,v,UFS);

      totcost += edge[i].cost;

    }

  }

  printf("%lld\n", totcost);

  return 0;

}

// Fastest known solution for this problem: