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#include <bits/stdc++.h>
using namespace std;
#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define rep(i, j) FOR(i, 0, j)
#define FORr(i, j, k) for(int i = j; i >= k; --i)
#define repr(i, j) FOR(i, j, 0)
#define INF (1 << 30)
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef pair<P, int> Pi;
const int MOD = 1e9 + 7;
const int dy[]={0, 0, 1, -1};
const int dx[]={1, -1, 0, 0};
template <class T> void chmin(T& a, const T& b) { a = min(a, b); }
template <class T> void chmax(T& a, const T& b) { a = max(a, b); }
struct edge { int u, v, cost; };
bool comp(const edge& e1, const edge& e2) {
return e1.cost < e2.cost;
}
int N;
vector<P> vx, vy;
vector<edge> es;
int par[100001], rk[100001];
ll res = 0;
void init(int n) {
rep(i, n) {
par[i] = i;
rk[i] = 0;
}
}
int find(int x) {
if(par[x] == x) return x;
else return par[x] = find(par[x]);
}
void unite(int x, int y) {
x = find(x);
y = find(y);
if(x == y) return;
if(rk[x] < rk[y]) par[x] = y;
else par[y] = x;
if(rk[x] == rk[y]) ++rk[x];
}
bool same(int x, int y) {
return find(x) == find(y);
}
void kruskal() {
sort(es.begin(), es.end(), comp);
init(N);
rep(i, es.size()) {
edge e = es[i];
if(!same(e.u, e.v)) {
unite(e.u, e.v);
res += e.cost;
}
}
}
int main() {
scanf("%d", &N);
rep(i, N) {
int X, Y;
scanf("%d %d", &X, &Y);
vx.push_back(P(X, i)); vy.push_back(P(Y, i));
}
sort(vx.begin(), vx.end()); sort(vy.begin(), vy.end());
FOR(i, 1, vx.size()) {
es.push_back({vx[i - 1].second, vx[i].second, vx[i].first - vx[i - 1].first});
}
FOR(i, 1, vy.size()) {
es.push_back({vy[i - 1].second, vy[i].second, vy[i].first - vy[i - 1].first});
}
kruskal();
printf("%lld\n", res);
return 0;
}
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