
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Comparator;
import java.util.InputMismatchException;
import java.util.PriorityQueue;

public class Main {
	InputStream is;

	int __t__ = 1;
	int __f__ = 0;
	int __FILE_DEBUG_FLAG__ = __f__;
	String __DEBUG_FILE_NAME__ = "src/D1";

	FastScanner in;
	PrintWriter out;
	
	class UnionFindTree {
		int[] parent;
		
		public UnionFindTree(int n) {
			parent = new int[n];
			for (int i = 0; i < parent.length; i++) {
				parent[i] = i;
			}
		}
		
		public int find(int x) {
			if (parent[x] == x) return x;
			return parent[x] = find(parent[x]);
		}
		
		public boolean same(int x, int y) {
			return find(x) == find(y);
		}
		
		public void unite(int x, int y) {
			int xx = find(x), yy = find(y);
			if (xx == yy) return;
			parent[xx] = yy;
		}
	}
	
	class Point {
		int id;
		int x;
		int y;

		Point(int id, int x, int y) {
			this.id = id;
			this.x = x;
			this.y = y;
		}
		
		public String toString() {
			return "(" + x + ", " + y + ")";
		}
	}
	
	class Edge implements Comparable<Edge> {
		int from;
		int to;
		int weight;

		Edge(int from, int to, int weight) {
			this.from = from;
			this.to = to;
			this.weight = weight;
		}

		public int compareTo(Edge s) {
			return weight - s.weight;
		}

		public String toString() {
			return "(" + from + ", " + to + ", " + weight + ")";
		}
	}
	
	public void solve() {
		int N = in.nextInt();
		Point[] ps = new Point[N];
		for (int i = 0; i < N; i++) {
			ps[i] = new Point(i, in.nextInt(), in.nextInt());
		}
		Point[] ps_x = Arrays.copyOf(ps, N);
		Arrays.sort(ps_x, (p1, p2) -> (p1.x - p2.x));
		Point[] ps_y = Arrays.copyOf(ps, N);
		Arrays.sort(ps_y, (p1, p2) -> (p1.y - p2.y));
		
		UnionFindTree uft = new UnionFindTree(N);
		PriorityQueue<Edge> pq = new PriorityQueue<Edge>();
		
		for (int i = 0; i < N - 1; i++) {
			pq.add(new Edge(ps_x[i].id, ps_x[i+1].id, (ps_x[i+1].x - ps_x[i].x)));
			pq.add(new Edge(ps_y[i].id, ps_y[i+1].id, (ps_y[i+1].y - ps_y[i].y)));
		}
		
		long res = 0;
		while (!pq.isEmpty()) {
			Edge e = pq.poll();
			if (uft.same(e.from, e.to)) continue;
			
			res += e.weight;
			uft.unite(e.from, e.to);
		}
		System.out.println(res);
	}
	
	public void run() {
		if (__FILE_DEBUG_FLAG__ == __t__) {
			try {
				is = new FileInputStream(__DEBUG_FILE_NAME__);
			} catch (FileNotFoundException e) {
				// TODO 自動生成された catch ブロック
				e.printStackTrace();
			}
			System.out.println("FILE_INPUT!");
		} else {
			is = System.in;
		}
		in = new FastScanner(is);
		out = new PrintWriter(System.out);

		solve();
	}

	public static void main(String[] args) {
		new Main().run();
	}

	public void mapDebug(int[][] a) {
		System.out.println("--------map display---------");

		for (int i = 0; i < a.length; i++) {
			for (int j = 0; j < a[i].length; j++) {
				System.out.printf("%3d ", a[i][j]);
			}
			System.out.println();
		}

		System.out.println("----------------------------");
		System.out.println();
	}

	public void debug(Object... obj) {
		System.out.println(Arrays.deepToString(obj));
	}

	class FastScanner {
		private InputStream stream;
		private byte[] buf = new byte[1024];
		private int curChar;
		private int numChars;

		public FastScanner(InputStream stream) {
			this.stream = stream;
			//stream = new FileInputStream(new File("dec.in"));

		}

		int read() {
			if (numChars == -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}

		boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}

		boolean isEndline(int c) {
			return c == '\n' || c == '\r' || c == -1;
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		int[] nextIntArray(int n) {
			int[] array = new int[n];
			for (int i = 0; i < n; i++)
				array[i] = nextInt();

			return array;
		}

		int[][] nextIntMap(int n, int m) {
			int[][] map = new int[n][m];
			for (int i = 0; i < n; i++) {
				map[i] = in.nextIntArray(m);
			}
			return map;
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		long[] nextLongArray(int n) {
			long[] array = new long[n];
			for (int i = 0; i < n; i++)
				array[i] = nextLong();

			return array;
		}

		long[][] nextLongMap(int n, int m) {
			long[][] map = new long[n][m];
			for (int i = 0; i < n; i++) {
				map[i] = in.nextLongArray(m);
			}
			return map;
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		double[] nextDoubleArray(int n) {
			double[] array = new double[n];
			for (int i = 0; i < n; i++)
				array[i] = nextDouble();

			return array;
		}

		double[][] nextDoubleMap(int n, int m) {
			double[][] map = new double[n][m];
			for (int i = 0; i < n; i++) {
				map[i] = in.nextDoubleArray(m);
			}
			return map;
		}

		String next() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}

		String[] nextStringArray(int n) {
			String[] array = new String[n];
			for (int i = 0; i < n; i++)
				array[i] = next();

			return array;
		}

		String nextLine() {
			int c = read();
			while (isEndline(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isEndline(c));
			return res.toString();
		}
	}
}
