// template version 1.6
// {{{ define basic macro
using namespace std;
#include <iostream>
#include <bits/stdc++.h>
// varibable settings
#define int long long
#define INF 1000000000000000000LL
// #define INF 2147483647
#define MOD 1000000007LL
// #define MOD 998244353LL
#define infile "../test/sample-1.in"

#define _overload3(_1,_2,_3,name,...) name
#define _rep(i,n) repi(i,0,n)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__)
#define _rrep(i,n) rrepi(i,0,n)
#define rrepi(i,a,b) for(int i=(int)(b-1);i>=(int)(a);--i)
#define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define pb(a) push_back(a)
#define mp(a, b) make_pair(a, b)
#define uni(x) sort(all(x));x.erase(unique(all(x)),x.end())
#define ten(n) ((int)1e##n)
template<class T, size_t N> size_t sza(const T (&array)[N]) { return N; }
template<class T> inline void chmax(T &a, const T &b) { if(a < b) a = b; }
template<class T> inline void chmin(T &a, const T &b) { if(a > b) a = b; }
template<class T=int> T in() {T x; cin>>x; return (x);}
struct Fast { Fast(){ std::cin.tie(0); ios::sync_with_stdio(false); } } fast;

// dump macro
#ifdef PCM
  #include "dump.hpp"
#else
  #define dump(...) 42
  #define dump_1d(...) 42
  #define dump_2d(...) 42
#endif

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef long double ld;
typedef pair<int,int> pii;
typedef tuple<int,int,int> iii;
template<typename T> using PQ = priority_queue<T, vector<T>, greater<T>>;
int dx[]={1, -1, 0, 0};
int dy[]={0, 0, 1, -1};
#define fi first
#define se second

// }}}

int n;
vector<iii> sx, sy;

//BEGIN CUT HERE{{{
struct Kruskal{

  struct UnionFind{
    int n;
    vector<int> r,p;
    UnionFind(){}
    UnionFind(int sz):n(sz),r(sz,1),p(sz,0){iota(p.begin(),p.end(),0);}
    int find(int x){
      return (x==p[x]?x:p[x]=find(p[x]));
    }
    bool same(int x,int y){
      return find(x)==find(y);
    }
    void unite(int x,int y){
      x=find(x);y=find(y);
      if(x==y) return;
      if(r[x]<r[y]) swap(x,y);
      r[x]+=r[y];
      p[y]=x;
    }
  };

  struct edge{
    int from,to,cost,used;
    edge(){}
    edge(int from,int to,int cost):
      from(from),to(to),cost(cost),used(0){}
    bool operator<(const edge& e) const{
      return cost<e.cost;
    }
  };

  int n;
  vector<edge> edges;

  Kruskal(){}
  Kruskal(int sz):n(sz){}

  void add_edge(int u,int v,int c){
    edges.emplace_back(u,v,c);
  }

  void input(int n, int offset=0){
    rep(i, 1, n){
      add_edge(get<0>(sx[i]), get<0>(sx[i-1]), get<1>(sx[i])-get<1>(sx[i-1]));
      add_edge(get<0>(sx[i-1]), get<0>(sx[i]), get<1>(sx[i])-get<1>(sx[i-1]));
      add_edge(get<0>(sy[i]), get<0>(sy[i-1]), get<2>(sy[i])-get<2>(sy[i-1]));
      add_edge(get<0>(sy[i-1]), get<0>(sy[i]), get<2>(sy[i])-get<2>(sy[i-1]));
    }
  }

  int build(){
    sort(edges.begin(),edges.end());
    UnionFind uf(n+1);
    int res=0;
    for(auto &e:edges){
      if(!uf.same(e.from,e.to)){
        res+=e.cost;
        uf.unite(e.from,e.to);
        e.used=1;
      }
    }
    return res;
  }
};
//END CUT HERE}}}

int solve(){
  cin>>n;
  int x[n];
  int y[n];
  rep(i, n){
    cin>>x[i]>>y[i];
    sx.pb(make_tuple(i, x[i], y[i]));
    sy.pb(make_tuple(i, x[i], y[i]));
  }
  sort(all(sx), [](auto &left, auto &right){return get<1>(left) < get<1>(right);});
  sort(all(sy), [](auto &left, auto &right){return get<2>(left) < get<2>(right);});
  dump(sx);
  dump(sy);

  rep(i, n){
  }

  Kruskal kruskal(n);
  kruskal.input(n);
  cout<<kruskal.build()<<endl;

  return 0;
}

signed main() { //{{{
#ifdef INPUT_FROM_FILE
  std::ifstream in(infile);
  std::cin.rdbuf(in.rdbuf());
#endif
  solve();
  return 0;
} //}}}


Measured memory_bytes: 27548