#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<string>
#include<cmath>
#include<map>
#include<set>
#include<vector>
#include<queue>
#include<bitset>
#include<ctime>
#include<deque>
#include<stack>
#include<functional>
#include<sstream>
//#include<cctype>
//#pragma GCC optimize(2)
using namespace std;
#define maxn 2000005
#define inf 0x7fffffff
//#define INF 1e18
#define rdint(x) scanf("%d",&x)
#define rdllt(x) scanf("%lld",&x)
#define rdult(x) scanf("%lu",&x)
#define rdlf(x) scanf("%lf",&x)
#define rdstr(x) scanf("%s",x)
typedef long long  ll;
typedef unsigned long long ull;
typedef unsigned int U;
#define ms(x) memset((x),0,sizeof(x))
const long long int mod = 1e9 + 7;
#define Mod 1000000000
#define sq(x) (x)*(x)
#define eps 1e-4
typedef pair<int, int> pii;
#define pi acos(-1.0)
//const int N = 1005;
#define REP(i,n) for(int i=0;i<(n);i++)
typedef pair<int, int> pii;
inline ll rd() {ll x = 0;char c = getchar();bool f = false;while (!isdigit(c)) {if (c == '-') f = true;c = getchar();}while (isdigit(c)) {x = (x << 1) + (x << 3) + (c ^ 48);c = getchar();}return f ? -x : x;
}ll gcd(ll a, ll b) {return b == 0 ? a : gcd(b, a%b);
}
int sqr(int x) { return x * x; }/*ll ans;
ll exgcd(ll a, ll b, ll &x, ll &y) {if (!b) {x = 1; y = 0; return a;}ans = exgcd(b, a%b, x, y);ll t = x; x = y; y = t - a / b * y;return ans;
}
*/int n;
int tot;
struct node {int x, y;int d;node(){}node(int x,int y,int d):x(x),y(y),d(d){}}nd[maxn],nd2[maxn];bool cmp(node a, node b) {return a.x < b.x;
}
bool cmp2(node a, node b) {return a.y < b.y;
}bool cmp3(node a, node b) {return a.d < b.d;
}int fa[maxn];
void init() {for (int i = 0; i <= n; i++)fa[i] = i;
}
int findfa(int x) {if (x == fa[x])return x;return fa[x] = findfa(fa[x]);
}void merge(int u, int v) {int p = findfa(u);int q = findfa(v);if (p != q) {fa[p] = q;}
}bool chk(int x, int y) {if (findfa(x) == findfa(y))return true;else return false;
}int kruskal() {int sum = 0;init();for (int i = 0; i < tot; i++) {node tmp = nd2[i];if (tmp.d == 0)merge(tmp.x, tmp.y);if (!chk(tmp.x, tmp.y)) {merge(tmp.x, tmp.y); sum += tmp.d;}}return sum;
}int main() {
//  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);cin >> n;for (int i = 1; i <= n; i++) {rdint(nd[i].x); rdint(nd[i].y);nd[i].d = i;}tot = 0;sort(nd + 1, nd + 1 + n, cmp);for (int i = 2; i <= n; i++) {nd2[tot++] = node(nd[i].d, nd[i - 1].d, nd[i].x - nd[i - 1].x);}sort(nd+1, nd + n+1, cmp2);for (int i = 2; i <= n; i++) {nd2[tot++] = node(nd[i].d, nd[i - 1].d, nd[i].y - nd[i - 1].y);}sort(nd2, nd2 + tot, cmp3);int sum = kruskal();cout << sum << endl;return 0;
}