package main

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"math"
	"os"
	"sort"
	"strconv"
)

/*********** I/O ***********/

var (
	// ReadString returns a WORD string.
	ReadString func() string
	stdout     *bufio.Writer
)

func init() {
	ReadString = newReadString(os.Stdin)
	stdout = bufio.NewWriter(os.Stdout)
}

func newReadString(ior io.Reader) func() string {
	r := bufio.NewScanner(ior)
	// r.Buffer(make([]byte, 1024), int(1e+11)) // for AtCoder
	r.Buffer(make([]byte, 1024), int(1e+9)) // for Codeforces
	// Split sets the split function for the Scanner. The default split function is ScanLines.
	// Split panics if it is called after scanning has started.
	r.Split(bufio.ScanWords)

	return func() string {
		if !r.Scan() {
			panic("Scan failed")
		}
		return r.Text()
	}
}

// ReadInt returns an integer.
func ReadInt() int {
	return int(readInt64())
}
func ReadInt2() (int, int) {
	return int(readInt64()), int(readInt64())
}
func ReadInt3() (int, int, int) {
	return int(readInt64()), int(readInt64()), int(readInt64())
}
func ReadInt4() (int, int, int, int) {
	return int(readInt64()), int(readInt64()), int(readInt64()), int(readInt64())
}

// ReadInt64 returns as integer as int64.
func ReadInt64() int64 {
	return readInt64()
}
func ReadInt64_2() (int64, int64) {
	return readInt64(), readInt64()
}
func ReadInt64_3() (int64, int64, int64) {
	return readInt64(), readInt64(), readInt64()
}
func ReadInt64_4() (int64, int64, int64, int64) {
	return readInt64(), readInt64(), readInt64(), readInt64()
}

func readInt64() int64 {
	i, err := strconv.ParseInt(ReadString(), 0, 64)
	if err != nil {
		panic(err.Error())
	}
	return i
}

// ReadIntSlice returns an integer slice that has n integers.
func ReadIntSlice(n int) []int {
	b := make([]int, n)
	for i := 0; i < n; i++ {
		b[i] = ReadInt()
	}
	return b
}

// ReadInt64Slice returns as int64 slice that has n integers.
func ReadInt64Slice(n int) []int64 {
	b := make([]int64, n)
	for i := 0; i < n; i++ {
		b[i] = ReadInt64()
	}
	return b
}

// ReadFloat64 returns an float64.
func ReadFloat64() float64 {
	return float64(readFloat64())
}

func readFloat64() float64 {
	f, err := strconv.ParseFloat(ReadString(), 64)
	if err != nil {
		panic(err.Error())
	}
	return f
}

// ReadFloatSlice returns an float64 slice that has n float64.
func ReadFloat64Slice(n int) []float64 {
	b := make([]float64, n)
	for i := 0; i < n; i++ {
		b[i] = ReadFloat64()
	}
	return b
}

// ReadRuneSlice returns a rune slice.
func ReadRuneSlice() []rune {
	return []rune(ReadString())
}

/*********** Debugging ***********/

// ZeroPaddingRuneSlice returns binary expressions of integer n with zero padding.
// For debugging use.
func ZeroPaddingRuneSlice(n, digitsNum int) []rune {
	sn := fmt.Sprintf("%b", n)

	residualLength := digitsNum - len(sn)
	if residualLength <= 0 {
		return []rune(sn)
	}

	zeros := make([]rune, residualLength)
	for i := 0; i < len(zeros); i++ {
		zeros[i] = '0'
	}

	res := []rune{}
	res = append(res, zeros...)
	res = append(res, []rune(sn)...)

	return res
}

// Strtoi is a wrapper of strconv.Atoi().
// If strconv.Atoi() returns an error, Strtoi calls panic.
func Strtoi(s string) int {
	if i, err := strconv.Atoi(s); err != nil {
		panic(errors.New("[argument error]: Strtoi only accepts integer string"))
	} else {
		return i
	}
}

// PrintIntsLine returns integers string delimited by a space.
func PrintIntsLine(A ...int) string {
	res := []rune{}

	for i := 0; i < len(A); i++ {
		str := strconv.Itoa(A[i])
		res = append(res, []rune(str)...)

		if i != len(A)-1 {
			res = append(res, ' ')
		}
	}

	return string(res)
}

// PrintIntsLine returns integers string delimited by a space.
func PrintInts64Line(A ...int64) string {
	res := []rune{}

	for i := 0; i < len(A); i++ {
		str := strconv.FormatInt(A[i], 10) // 64bit int version
		res = append(res, []rune(str)...)

		if i != len(A)-1 {
			res = append(res, ' ')
		}
	}

	return string(res)
}

// PrintDebug is wrapper of fmt.Fprintf(os.Stderr, format, a...)
func PrintDebug(format string, a ...interface{}) {
	fmt.Fprintf(os.Stderr, format, a...)
}

/********** FAU standard libraries **********/

//fmt.Sprintf("%b\n", 255) 	// binary expression

/********** I/O usage **********/

//str := ReadString()
//i := ReadInt()
//X := ReadIntSlice(n)
//S := ReadRuneSlice()
//a := ReadFloat64()
//A := ReadFloat64Slice(n)

//str := ZeroPaddingRuneSlice(num, 32)
//str := PrintIntsLine(X...)

/*
ASCII code

ASCII   10進数  ASCII   10進数  ASCII   10進数
!       33      "       34      #       35
$       36      %       37      &       38
'       39      (       40      )       41
*       42      +       43      ,       44
-       45      .       46      /       47
0       48      1       49      2       50
3       51      4       52      5       53
6       54      7       55      8       56
9       57      :       58      ;       59
<       60      =       61      >       62
?       63      @       64      A       65
B       66      C       67      D       68
E       69      F       70      G       71
H       72      I       73      J       74
K       75      L       76      M       77
N       78      O       79      P       80
Q       81      R       82      S       83
T       84      U       85      V       86
W       87      X       88      Y       89
Z       90      [       91      \       92
]       93      ^       94      _       95
`       96      a       97      b       98
c       99      d       100     e       101
f       102     g       103     h       104
i       105     j       106     k       107
l       108     m       109     n       110
o       111     p       112     q       113
r       114     s       115     t       116
u       117     v       118     w       119
x       120     y       121     z       122
{       123     |       124     }       125
~       126             127
*/

/*******************************************************************/

const (
	// General purpose
	MOD          = 1000000000 + 7
	ALPHABET_NUM = 26
	INF_INT64    = math.MaxInt64
	INF_BIT60    = 1 << 60
	INF_INT32    = math.MaxInt32
	INF_BIT30    = 1 << 30
	NIL          = -1

	// for dijkstra, prim, and so on
	WHITE = 0
	GRAY  = 1
	BLACK = 2
)

var (
	n    int
	X, Y []int
)

type City struct {
	x, y, id int
}
type CityList []*City
type byX struct {
	CityList
}
type byY struct {
	CityList
}

func (l CityList) Len() int {
	return len(l)
}
func (l CityList) Swap(i, j int) {
	l[i], l[j] = l[j], l[i]
}

func (l byX) Less(i, j int) bool {
	return l.CityList[i].x < l.CityList[j].x
}
func (l byY) Less(i, j int) bool {
	return l.CityList[i].y < l.CityList[j].y
}

// how to use
// L := make(CityList, 0, 200000+5)
// L = append(L, &City{key: intValue})
// sort.Stable(byKey{ L })                // Stable ASC
// sort.Stable(sort.Reverse(byKey{ L }))  // Stable DESC

func main() {
	n = ReadInt()
	L := make(CityList, 0)
	for i := 0; i < n; i++ {
		x, y := ReadInt2()
		L = append(L, &City{x: x, y: y, id: i})
	}

	edges := make(EdgeList, 0)

	sort.Stable(byX{L})
	for i := 1; i < n; i++ {
		cost := L[i].x - L[i-1].x
		edges = append(edges, &Edge{from: L[i].id, to: L[i-1].id, cost: cost})
	}
	sort.Stable(byY{L})
	for i := 1; i < n; i++ {
		cost := L[i].y - L[i-1].y
		edges = append(edges, &Edge{from: L[i].id, to: L[i-1].id, cost: cost})
	}

	sort.Stable(byKey{edges})

	uf := NewUnionFind(100000 + 5)
	ans := 0
	for i := 0; i < len(edges); i++ {
		e := edges[i]
		if !uf.Same(e.to, e.from) {
			ans += e.cost
			uf.Unite(e.to, e.from)
		}
	}

	fmt.Println(ans)
}

type Edge struct {
	from, to, cost int
}
type EdgeList []*Edge
type byKey struct {
	EdgeList
}

func (l EdgeList) Len() int {
	return len(l)
}
func (l EdgeList) Swap(i, j int) {
	l[i], l[j] = l[j], l[i]
}

func (l byKey) Less(i, j int) bool {
	return l.EdgeList[i].cost < l.EdgeList[j].cost
}

// 0-based
// uf := NewUnionFind(n)
// uf.Root(x) 			// Get root node of the node x
// uf.Unite(x, y) 	// Unite node x and node y
// uf.Same(x, y) 		// Judge x and y are in the same connected component.
// uf.CcSize(x) 		// Get size of the connected component including node x
// uf.CcNum() 			// Get number of connected components

// UnionFind provides disjoint set algorithm.
// Node id starts from 0 (0-based setting).
type UnionFind struct {
	parents []int
}

// NewUnionFind returns a pointer of a new instance of UnionFind.
func NewUnionFind(n int) *UnionFind {
	uf := new(UnionFind)
	uf.parents = make([]int, n)

	for i := 0; i < n; i++ {
		uf.parents[i] = -1
	}

	return uf
}

// Root method returns root node of an argument node.
// Root method is a recursive function.
func (uf *UnionFind) Root(x int) int {
	if uf.parents[x] < 0 {
		return x
	}

	// route compression
	uf.parents[x] = uf.Root(uf.parents[x])
	return uf.parents[x]
}

// Unite method merges a set including x and a set including y.
func (uf *UnionFind) Unite(x, y int) bool {
	xp := uf.Root(x)
	yp := uf.Root(y)

	if xp == yp {
		return false
	}

	// merge: xp -> yp
	// merge larger set to smaller set
	if uf.CcSize(xp) > uf.CcSize(yp) {
		xp, yp = yp, xp
	}
	// update set size
	uf.parents[yp] += uf.parents[xp]
	// finally, merge
	uf.parents[xp] = yp

	return true
}

// Same method returns whether x is in the set including y or not.
func (uf *UnionFind) Same(x, y int) bool {
	return uf.Root(x) == uf.Root(y)
}

// CcSize method returns the size of a set including an argument node.
func (uf *UnionFind) CcSize(x int) int {
	return -uf.parents[uf.Root(x)]
}

// CcNum method returns the number of connected components.
// Time complextity is O(n)
func (uf *UnionFind) CcNum() int {
	res := 0
	for i := 0; i < len(uf.parents); i++ {
		if uf.parents[i] < 0 {
			res++
		}
	}
	return res
}

// how to use
// L := make(EdgeList, 0, 200000+5)
// L = append(L, &Edge{key: intValue})
// sort.Stable(byKey{ L })                // Stable ASC
// sort.Stable(sort.Reverse(byKey{ L }))  // Stable DESC

// 1. ソート可能なエッジリストを構成する。
//   - エッジ構造体は |from, to, cost| を最低限備えていれば良い。
// 2. エッジリストをコストで昇順ソートする。
// 3. 閉路判定用のUF木を確保する。
//   - 確保するノード数は最大値を適当に超えさせておけば良い。
// 4. エッジリストを先頭からチェックし |!uf.Same(e.from, e.to)| を満たすもののコストだけ答えに加算する。

/*
- まずは全探索を検討しましょう
- MODは最後にとりましたか？
- ループを抜けた後も処理が必要じゃありませんか？
- 和・積・あまりを求められたらint64が必要ではありませんか？
- いきなりオーバーフローはしていませんか？
- MOD取る系はint64必須ですよ？
- 後ろ・逆・ゴールから考えましたか？
- 3者のうち真ん中に着目しましたか？
*/

/*******************************************************************/


Measured memory_bytes: 18432