import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class Main {

	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		MyInput in = new MyInput(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		TaskX solver = new TaskX();
		solver.solve(1, in, out);
		out.close();
	}

	static int INF = 1 << 30;
	static long LINF = 1L << 55;
	static int MOD = 1000000007;
	static int[] mh4 = { 0, -1, 1, 0 };
	static int[] mw4 = { -1, 0, 0, 1 };
	static int[] mh8 = { -1, -1, -1, 0, 0, 1, 1, 1 };
	static int[] mw8 = { -1, 0, 1, -1, 1, -1, 0, 1 };

	static class TaskX {

		public void solve(int testNumber, MyInput in, PrintWriter out) {

			int n = in.nextInt();
			P[] p = new P[n];
			for (int i = 0; i < n; i++) {
				int x = in.nextInt(), y = in.nextInt();
				p[i] = new P(i, x, y);
			}

			List<T> list = new ArrayList<>();

			Arrays.sort(p, (p1, p2) -> p1.x - p2.x);
			for (int i = 0; i < n-1; i++) {
				list.add(new T(p[i+1].idx, p[i].idx, p[i+1].x - p[i].x));
			}

			Arrays.sort(p, (p1, p2) -> p1.y - p2.y);
			for (int i = 0; i < n-1; i++) {
				list.add(new T(p[i+1].idx, p[i].idx, p[i+1].y - p[i].y));
			}

			Collections.sort(list);

			long ans = 0;
			UnionFind uf = new UnionFind(2 * n);
			for (int i = 0; i < list.size(); i++) {
				if (uf.same(list.get(i).s, list.get(i).t)) continue;
				uf.union(list.get(i).s, list.get(i).t);
				ans += list.get(i).w;
			}

			out.println(ans);
		}

		class P {
			int idx, x, y;

			public P(int idx, int x, int y) {
				super();
				this.idx = idx;
				this.x = x;
				this.y = y;
			}


			@Override
			public String toString() {
				return "P [x=" + x + ", y=" + y + "]";
			}
		}

		class T implements Comparable<T> {
			int s, t;
			long w;
			public T(int s, int t, long w) {
				super();
				this.s = s;
				this.t = t;
				this.w = w;
			}
			@Override
			public String toString() {
				return "Edge [s=" + s + ", t=" + t + ", w=" + w + "]";
			}

			@Override
			public int compareTo(T o) {
				return Long.compare(this.w, o.w);
			}
		}
	}

	static class UnionFind {
		int[] data;

		public UnionFind(int size) {
			data = new int[size];
			clear();
		}

		public void clear() {
			Arrays.fill(data, -1);
		}

		public int root(int x) {
			return data[x] < 0 ? x : (data[x] = root(data[x]));
		}

		public void union(int x, int y) {
			x = root(x);
			y = root(y);

			if (x != y) {
				if (data[y] > data[x]) {
					final int t = x;
					x = y;
					y = t;
				}

				data[x] += data[y];
				data[y] = x;
			}
		}

		boolean same(int x, int y) {
			return root(x) == root(y);
		}

		public int size(int x) {
			return -data[root(x)];
		}
	}

	static class MyInput {
		private final BufferedReader in;
		private static int pos;
		private static int readLen;
		private static final char[] buffer = new char[1024 * 8];
		private static char[] str = new char[500 * 8 * 2];
		private static boolean[] isDigit = new boolean[256];
		private static boolean[] isSpace = new boolean[256];
		private static boolean[] isLineSep = new boolean[256];

		static {
			for (int i = 0; i < 10; i++) {
				isDigit['0' + i] = true;
			}
			isDigit['-'] = true;
			isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true;
			isLineSep['\r'] = isLineSep['\n'] = true;
		}

		public MyInput(InputStream is) {
			in = new BufferedReader(new InputStreamReader(is));
		}

		public int read() {
			if (pos >= readLen) {
				pos = 0;
				try {
					readLen = in.read(buffer);
				} catch (IOException e) {
					throw new RuntimeException();
				}
				if (readLen <= 0) {
					throw new MyInput.EndOfFileRuntimeException();
				}
			}
			return buffer[pos++];
		}

		public int nextInt() {
			int len = 0;
			str[len++] = nextChar();
			len = reads(len, isSpace);
			int i = 0;
			int ret = 0;
			if (str[0] == '-') {
				i = 1;
			}
			for (; i < len; i++)
				ret = ret * 10 + str[i] - '0';
			if (str[0] == '-') {
				ret = -ret;
			}
			return ret;
		}

		public long nextLong() {
			int len = 0;
			str[len++] = nextChar();
			len = reads(len, isSpace);
			int i = 0;
			long ret = 0;
			if (str[0] == '-') {
				i = 1;
			}
			for (; i < len; i++)
				ret = ret * 10 + str[i] - '0';
			if (str[0] == '-') {
				ret = -ret;
			}
			return ret;
		}

		public char nextChar() {
			while (true) {
				final int c = read();
				if (!isSpace[c]) {
					return (char) c;
				}
			}
		}

		public String nextString() {
			return new String(nextChars());
		}

		public char[] nextChars() {
			int len = 0;
			str[len++] = nextChar();
			len = reads(len, isSpace);
			return Arrays.copyOf(str, len);
		}

		public char[][] next2DChars(int h, int w) {
			char[][] s = new char[h][w];
			for (int i = 0; i < h; i++) {
				s[i] = nextChars();
			}
			return s;
		}

		int reads(int len, boolean[] accept) {
			try {
				while (true) {
					final int c = read();
					if (accept[c]) {
						break;
					}
					if (str.length == len) {
						char[] rep = new char[str.length * 3 / 2];
						System.arraycopy(str, 0, rep, 0, str.length);
						str = rep;
					}
					str[len++] = (char) c;
				}
			} catch (MyInput.EndOfFileRuntimeException e) {
			}
			return len;
		}

		public int[] nextIntArray(final int n) {
			final int[] res = new int[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextInt();
			}
			return res;
		}

		public int[] nextIntArray1Index(final int n) {
			final int[] res = new int[n + 1];
			for (int i = 1; i < n + 1; i++) {
				res[i] = nextInt();
			}
			return res;
		}

		public int[] nextIntArrayDec(final int n) {
			final int[] res = new int[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextInt() - 1;
			}
			return res;
		}

		public long[] nextLongArray(final int n) {
			final long[] res = new long[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextLong();
			}
			return res;
		}

		public long[] nextLongArray1Index(final int n) {
			final long[] res = new long[n + 1];
			for (int i = 1; i < n + 1; i++) {
				res[i] = nextLong();
			}
			return res;
		}

		public long[] nextLongArrayDec(final int n) {
			final long[] res = new long[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextLong() - 1;
			}
			return res;
		}

		public double nextDouble() {
			return Double.parseDouble(nextString());
		}

		public double[] nextDoubleArray(int n) {
			double[] res = new double[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextDouble();
			}
			return res;
		}

		static class EndOfFileRuntimeException extends RuntimeException {
		}

	}

}


Measured memory_bytes: 55916