#include <bits/stdc++.h>
#define rep(i,n) for (int i = (0); i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define rng(x) (x).begin(),(x).end()
#define rrng(x) (x).rbegin(),(x).rend()
#define limit(x,l,r) max(l,min(x,r))
#define lims(x,l,r) (x = max(l,min(x,r)))
#define isin(x,l,r) ((l) <= (x) && (x) < (r))
#define show(x) cout << #x << " = " << (x) << endl
#define show2(x,y) cout << #x << " = " << (x) << ", " << #y << " = " << (y) << endl
#define show3(x,y,z) cout << #x << " = " << (x) << ", " << #y << " = " << (y) <<  ", " << #z << " = " << (z) << endl
#define showv(v) rep(i,v.size()) printf("%d%c", v[i], i==v.size()-1?'\n':' ')
#define showv2(v) rep(j,v.size()) showv(v[j])
#define showt(t,n) rep(i,n) printf("%d%c", t[i], i==n-1?'\n':' ')
#define showt2(t,r,c) rep(j,r) showt(t[j],c)
#define showvp(p) rep(i,p.size()) printf("%d %d\n", p[i].first, p[i].second);
#define printv(v) rep(i,v.size()) printf("%d\n", v[i])
#define printt(t,n) rep(i,n) printf("%d\n", t[i])
#define incl(v,x) find(rng(v),x)!=v.end()
#define incls(s,c) s.find(c)!=string::npos
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define bit(n,k) ((n>>k)&1) // nのk bit目
#define bn(x) ((1<<x)-1)
#define dup(x,y) (((x)+(y)-1)/(y))
#define newline puts("")
#define uni(x) x.erase(unique(rng(x)),x.end())
#define SP << " " <<
#define v(T) vector<T>
#define vv(T) v(v(T))
using namespace std;
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vs = vector<string>;
using P = pair<int, int>;
using T = tuple<int, int, int>;
using vp = vector<P>;
using vt = vector<T>;
const int mod = 1000000007;
const double EPS = 1e-9;
//const long double EPS = 1e-14;
const int INF = (1<<30)-1;
const ll LINF = (1LL<<62)-1;
#define dame { puts("No"); return 0;}
#define yn {puts("Yes");}else{puts("No");}
inline int in() { int x; scanf("%d",&x); return x;}
inline ll lin() { ll x; scanf("%lld",&x); return x;}
inline char chin() { char x; scanf("%c",&x); return x;}
inline string stin() { string x; cin >> x; return x;}
inline double din() { double x; scanf("%lf",&x); return x;}
//template<class T = int> inline T in() { T x; cin >> x; return (x);}
template<typename T>inline ll suma(const v(T)& a) { ll res(0); for (auto&& x : a) res += x; return res;}
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; }
char itoa(int n) { return n + '0';}
ll gcd(ll a, ll b) { return b ? gcd(b,a%b) : a;}
ll lcm(ll a, ll b) { return a/gcd(a,b)*b;}

const int MAX_V = 200005;
const int MAX_E = 200005;
int V; // 頂点数
int E; // 辺の本数

struct edge{ int u, v, cost;};
edge es[MAX_E];

struct UnionFind {
  vector<int> d;
  UnionFind(int n): d(n,-1) {}
  int find(int x) {
    if (d[x] < 0) return x;
    return d[x] = find(d[x]);
  }
  bool unite(int x, int y) {
    x = find(x); y = find(y);
    if (x == y) return false;
    if (d[x] > d[y]) swap(x,y); // -d[x] < -d[y]
    d[x] += d[y];
    d[y] = x;
    return true;
  }
  bool same(int x, int y) { return find(x) == find(y);}
  int size(int x) { return -d[find(x)];}
};

// クラスカル法: 最小全域木のコストの合計値を返す O(|E|log|V|)
int kruskal() {
  auto comp = [](const edge& e1, const edge& e2) {
    return e1.cost < e2.cost;
  };
  sort(es, es + E, comp);
  UnionFind uf(MAX_V);
  int res = 0;
  for (int i = 0; i < E; ++i) {
    edge e = es[i];
    if (!uf.same(e.u, e.v)) {
      uf.unite(e.u, e.v);
      res += e.cost;
    }
  }
  return res;
}

int main () {
  int n;
  cin >> n;
  vt p(n);
  rep(i,n) {
    int x, y;
    cin >> x >> y;
    x--, y--;
    p[i] = make_tuple(x,y,i);
  }
  auto q = p;
  sort(rng(p));

  auto comp_y = [&](T a, T b) {
    if (get<1>(a) != get<1>(b)) return get<1>(a) < get<1>(b);
    else return get<0>(a) < get<0>(b);
  };
  sort(rng(q),comp_y);

  V = 2*n;
  E = 2*(n-1);
  rep(i,n-1) {
    es[2*i] = (edge){get<2>(p[i]), get<2>(p[i+1]), abs(get<0>(p[i])-get<0>(p[i+1]))};
    es[2*i+1] = (edge){get<2>(q[i]), get<2>(q[i+1]), abs(get<1>(q[i])-get<1>(q[i+1]))};
  }
  int ans = kruskal();
  cout << ans << endl;
  return 0;
}

Measured memory_bytes: 5760