// Slower C++ solution:
#include<iostream>

#include<fstream>

#include<sstream>

#include<algorithm>

#include<cstdio>

#include<cassert>

#include<cmath>

#include<cstdlib>

#include<cstring>

#include<string>

#include<deque>

#include<queue>

#include<vector>

#include<list>

#include<map>

#include<set>

#include<bitset>

#include<stack>

#include<iomanip>

#include<utility>

#include<functional>

using namespace std;

int n,m;

int ans;

int par[100005];

vector<int> edge[100005];

vector<pair<int,int> > el;

pair<int,int> e[200005];

pair<pair<int,int>,int> a[100005],b[100005];

int find(int x)

{

	if(par[x]!=x)

		return par[x]=find(par[x]);

	else

		return par[x];

}

bool unite(int x,int y)

{

	x=find(x);

	y=find(y);

	if(x==y)

		return false;

	else

	{

		par[x]=y;

		return true;

	}

}

int main()

{

	cin>>n;

	for(int i=0;i<n;i++)

	{

		cin>>a[i].first.first>>a[i].first.second;

		b[i].first.first=a[i].first.second;

		b[i].first.second=a[i].first.first;

		a[i].second=b[i].second=i;

	}

	sort(a,a+n);

	sort(b,b+n);

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

	{

		edge[a[i].second].push_back(a[i-1].second);

		e[m]=make_pair(a[i].second,a[i-1].second);

		el.push_back(make_pair(a[i].first.first-a[i-1].first.first,m++));

	}

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

	{

		edge[b[i].second].push_back(b[i-1].second);

		e[m]=make_pair(b[i].second,b[i-1].second);

		el.push_back(make_pair(b[i].first.first-b[i-1].first.first,m++));

	}

	for(int i=0;i<n;i++)

		par[i]=i;

	sort(el.begin(),el.end());

	for(int i=0;i<m;i++)

	{

		int xx=e[el[i].second].first;

		int yy=e[el[i].second].second;

		if(unite(xx,yy))

			ans+=el[i].first;

	}

	cout<<ans;

	return 0;

}


// Faster C++ solution for the same problem (measured speedup: 2.4852435175162206x):
#include <bits/stdc++.h>

using namespace std;



#define ENGZ ios::sync_with_stdio(0);cin.tie(0);ios_base::sync_with_stdio(0);

#define sfi(x) scanf("%d" , &x)

#define sfi2(x, y) scanf("%d%d" , &x,&y)

#define sfl2(x, y) scanf("%I64d%I64d" , &x,&y)

#define sfl(x) scanf("%I64d" , &x)

#define sfl3(x, y, z) scanf("%I64d%I64d%I64d", &x, &y, &z)

#define sfd(x) scanf("%lf", &x)

#define sfd2(x, y) scanf("%lf", &x, &y)

#define sfs(x) scanf("%s", &x)

#define testv(x) cerr << x << ' '

#define wtf(s) freopen((s), "w", stdout)

#define rff(s) freopen((s), "r", stdin)

#define test cerr << "here"

#define fst(x) cout << fixed << setprecision(x)

#define mod 1000000007

#define pi (2 * acos(0))

typedef long double ld;

typedef long long ll;



int par[200005], rnk[200005];



int findp(int x)

{

    if (par[x] == x)

        return x;

    return par[x] = findp(par[x]);

}



bool iscon(int x, int y)

{

    if (findp(x) == findp(y))

        return true;

    return false;

}



void con(int x, int y)

{

    int px = findp(x), py = findp(y);

    if (rnk[px] > rnk[py])

        par[py] = px;

    else if (rnk[px] < rnk[py])

        par[px] = py;

    else

        par[px] = py, rnk[px]++;

}





    pair<pair<ll, ll>, int> a[100005], b[100005];

int main()

{

    ENGZ

    int n;

    ll ans = 0;

    for (int i = 0; i < 100005; i++)

        par[i] = i;

    cin >> n;

    for (int i = 0; i < n; i++)

    {

        cin >> a[i].first.first >> a[i].first.second;

        b[i].first.first = a[i].first.second;

        b[i].first.second = a[i].first.first;

        a[i].second = b[i].second = i;

    }

    sort(a, a + n);

    sort(b, b + n);

    map<ll, vector<pair<int, int>>> mp;

    for (int i = 0; i < n - 1; i++)

    {

        mp[abs(a[i].first.first - a[i + 1].first.first)].push_back({a[i].second, a[i + 1].second});

        mp[abs(b[i].first.first - b[i + 1].first.first)].push_back({b[i].second, b[i + 1].second});

    }

    for (auto it: mp)

    {

        for (auto i: it.second)

        {

            if (!iscon(i.first, i.second))

                con(i.first, i.second), ans += it.first;

        }

    }

    cout << ans;

    return 0;

}