#include<bits/stdc++.h>
using namespace std;

#define rep(i,n) for(long long i=0;i<n;i++)
#define REP(i,s,n) for(long long i=(s);i<=(n);i++)
#define repr(i,n) for(long long i=n-1;i>=0;i--)
#define REPR(i,s,n) for(long long i=(s);i>=(n);i--)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define Eunique(v) v.erase(unique(all(v)),v.end())
#define Eback(s) s.erase(s.end()-1,s.end())
#define minvec(v) *min_element(all(v))
#define maxvec(v) *max_element(all(v))
#define sumvec(v) accumulate(all(v),0LL)
#define pb push_back
#define pf push_front
#define m_p make_pair
#define DOUBLE fixed << setprecision(15)
#define OK cerr<<"OK\n"
#define OK1 cerr<<"OK1\n"
#define OK2 cerr<<"OK2\n"
#define sz(s) (long long)s.size()
#define INF ((1LL<<62)-(1LL<<31))
#define zero(x,n) setw(x) << setfill('0') << n
//#define endl '\n'

typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<long long> vll;
typedef vector<double> vd;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<string> vs;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef vector<vd> vvd;
typedef vector<vc> vvc;
typedef vector<vb> vvb;
typedef pair<ll,ll> P;
typedef vector<P> vP;

template<class A, class B>
ostream& operator<<(ostream& ost, const pair<A, B>&p) {
    ost << "{" << p.first << ", " << p.second << "} ";
    return ost;
}

template<class T>
ostream& operator<<(ostream& ost, const vector<T>&v) {
    ost << "{";
    for (int i = 0; i<(int)v.size(); i++) {
        if (i)ost << " ";
        ost << v[i];
    }
    ost << "} \n";
    return ost;
}

template<class A, class B>
ostream& operator<<(ostream& ost, const map<A, B>&v) {
    ost << "{";
    for (auto p:v) {
        ost << "{" << p.first << ", " << p.second << "} ";
    }
    ost << "} ";
    return ost;
}

void out(){cout << "\n";}
template<class T,class... Args>
void out(const T &x,const Args &... args){
    cout << x << " ";
    out(args...);
}

template<typename T>
istream& operator >> (istream& is, vector<T>& vec){
    for(T& e: vec) is >> e;
    return is;
}

template<typename T>
string join(vector<T>& vec, string sep=" "){
    stringstream ss;
    for(int i=0;i<(int)vec.size();i++){
        ss << vec[i] << (i+1==(int)vec.size()?"\n":sep);
    }
    return ss.str();
}

template<class T>
inline bool chmax(T& a, T b){if(a<b){a=b;return true;} return false;}

template<class T>
inline bool chmin(T& a, T b){if(a>b){a=b;return true;} return false;}

#define INT(...) int __VA_ARGS__;IN(__VA_ARGS__)
#define LL(...) long long __VA_ARGS__;IN(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__;IN(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__;IN(__VA_ARGS__)
#define STR(...) string __VA_ARGS__;IN(__VA_ARGS__)
#define LD(...) long double __VA_ARGS__;IN(__VA_ARGS__)

void scan(int& a){ cin >> a; }
void scan(long long& a){ cin >> a; }
void scan(char& a){ cin >> a; }
void scan(double& a){ cin >> a; }
void scan(string& a){ cin >> a; }
void scan(long double& a){ cin >> a; }

void IN(){}
template<class Head,class... Tail> void IN(Head& head,Tail&... tail){ scan(head); IN(tail...); }

void YES(bool b) {cout << ((b)?"YES\n":"NO\n");}
void Yes(bool b) {cout << ((b)?"Yes\n":"No\n");}
void yes(bool b) {cout << ((b)?"yes\n":"no\n");}
void Yay(bool b) {cout << ((b)?"Yay!\n":":(\n");}

const long double pi = acos(-1.0);
//const ll mod=1000000007;
const ll mod=998244353;

ll powmod(ll a,ll b){ll c=1; while(b>0){ if(b&1){ c=a*c%mod; } a=a*a%mod; b>>=1; } return c;}
ll nCrmod(ll n,ll r){ll x=1,y=1; for(ll i=0;i<r;i++) {x=x*(n-i)%mod; y=y*(i+1)%mod; } return x*powmod(y,mod-2)%mod;}
ll gcd(ll a,ll b){ while(b){ ll c=b; b=a%b; a=c; } return a; }
ll lcm(ll a,ll b){ if(!a || !b) return 0; return a*b/gcd(a,b); }
vll divisor(ll x){ vll v; for(int i=1;i*i<=x;i++)if(x%i==0){ v.pb(i);if(i*i!=x)v.pb(x/i); } sort(all(v)); return v; };
map<ll,ll> prime_factor(ll n){ map<ll,ll> m; for(ll i=2;i*i<=n;i++){ while(n%i==0){ m[i]++; n/=i; } } if(n!=1) m[n]=1; return m; }

struct edge{
    long long u;
    long long v;
    long long cost;
};

struct UnionFind {
	vector<long long> par;
	UnionFind(long long size):par(size+1,-1){}
	bool unite(long long x,long long y){
		x=root(x);
        y=root(y);
		if (x!=y){
			if(par[y]<par[x]) swap(x,y);
			par[x]+=par[y];
            par[y]=x;
		}
		return x!=y;
	}
	bool same(long long x,long long y){
        return root(x)==root(y);
    }
	int root(long long x){
        return par[x]<0?x:par[x]=root(par[x]);
    }
	int size(long long x){
        return -par[root(x)];
    }
};

bool comp(const edge& e1,const edge& e2){
    return e1.cost < e2.cost;
}

int kruskal(int n,vector<edge> tr){
    sort(tr.begin(),tr.end(),comp);
    UnionFind tree(n);
    int ret=0;
    for(auto e:tr){
        if(!tree.same(e.u,e.v)){
            tree.unite(e.u,e.v);
            ret+=e.cost;
        }
    }
    return ret;
}

int main()
{
	LL(n);
	vP a(n), b(n);
	rep(i,n){
		cin >> a[i].first >> b[i].first;
		a[i].second = i;
		b[i].second = i;
	}
	sort(all(a));
	sort(all(b));
	vector<edge> G;
	rep(i, n - 1){
		G.push_back({a[i].second, a[i + 1].second, a[i + 1].first - a[i].first});
		G.push_back({b[i].second, b[i + 1].second, b[i + 1].first - b[i].first});
	}
	cout << kruskal(n, G) << endl;
    return 0;
}


Measured memory_bytes: 16592