### BUGGY CODE ###

#from collections import *
#from itertools import *
#from bisect import *
from heapq import *
#import copy
#N=int(input())
#X,Y=map(int,input().split()))
#S=list(map(int,input().split()))
#S=[list(map(int,input().split())) for i in range(N)]
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)

        if x == y:
            return

        if self.parents[x] > self.parents[y]:
            x, y = y, x

        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}

    def __str__(self):
        return '\n'.join('{}: {}'.format(r, self.members(r)) for r in self.roots())

N=int(input())

Xsort=[]
Ysort=[]
for i in range(N):
    X,Y=map(int,input().split())
    Xsort.append([X,i])
    Ysort.append([Y,i])
Xsort=sorted(Xsort,key=lambda x:x[0])
Ysort=sorted(Ysort,key=lambda x:x[0])
Nidxlst=[[0,0] for i in range(N)]
for i in range(N):
    idx=Xsort[i][1]
    Nidxlst[idx][0]=i
    idx=Ysort[i][1]
    Nidxlst[idx][1]=i





def main(i):
    x,y=Nidxlst[i]
    lst=[]
    if x>0:
        a=Xsort[x-1][1]
        m=Xsort[x][0]-Xsort[x-1][0]
        if not uf.same(i,a):
            lst.append([m,a])
    if x<N-1:
        a=Xsort[x+1][1]
        m=Xsort[x+1][0]-Xsort[x][0]
        if not uf.same(i,a):
            lst.append([m,a])
    if y>0:
        a=Ysort[y-1][1]
        m=Ysort[y][0]-Ysort[y-1][0]
        if not uf.same(i,a):
            lst.append([m,a])
    if y<N-1:
        a=Ysort[y+1][1]
        m=Ysort[y+1][0]-Ysort[y][0]
        if not uf.same(i,a):
            lst.append([m,a])
    if lst:
        lst=sorted(lst,key=lambda x:x[0])
        uf.union(i,lst[0][1])
        return(lst[0][0])
value=0
uf=UnionFind(N)
for i in range(N):
    m=main(i)
    if m:
        value+=m
    if uf.group_count()==1:
        break
print(value)


### FIXED CODE ###

#from collections import *
#from itertools import *
#from bisect import *
from heapq import *
#import copy
#N=int(input())
#X,Y=map(int,input().split()))
#S=list(map(int,input().split()))
#S=[list(map(int,input().split())) for i in range(N)]

N=int(input())

Xsort=[]
Ysort=[]
for i in range(N):
    X,Y=map(int,input().split())
    Xsort.append([X,i])
    Ysort.append([Y,i])
Xsort=sorted(Xsort,key=lambda x:x[0])
Ysort=sorted(Ysort,key=lambda x:x[0])
Nidxlst=[[0,0] for i in range(N)]
for i in range(N):
    idx=Xsort[i][1]
    Nidxlst[idx][0]=i
    idx=Ysort[i][1]
    Nidxlst[idx][1]=i



value=0
x,y=Nidxlst[0]
ittenai=set([i for i in range(1,N)])

stack=[]
heapify(stack)
setm=set()
dic={}
def main(x,y):
    if x>0:
        a=Xsort[x-1][1]
        if a in ittenai:
            m=Xsort[x][0]-Xsort[x-1][0]
            heappush(stack,m)
            if m in setm :
                dic[m].append(a)
            else:
                setm.add(m)
                dic.update({m:[a]})
    if x<N-1:
        a=Xsort[x+1][1]
        if a in ittenai:
            m=Xsort[x+1][0]-Xsort[x][0]
            heappush(stack,m)
            if m in setm :
                dic[m].append(a)
            else:
                setm.add(m)
                dic.update({m:[a]})
    if y>0:
        a=Ysort[y-1][1]
        if a in ittenai:
            m=Ysort[y][0]-Ysort[y-1][0]
            heappush(stack,m)
            if m in setm :
                dic[m].append(a)
            else:
                setm.add(m)
                dic.update({m:[a]})
    if y<N-1:
        a=Ysort[y+1][1]
        if a in ittenai:
            m=Ysort[y+1][0]-Ysort[y][0]
            heappush(stack,m)
            if m in setm :
                dic[m].append(a)
            else:
                setm.add(m)
                dic.update({m:[a]})
main(x,y)
idle=10**9+1
value=0
while ittenai:
    m=heappop(stack)
    a=dic[m].pop()
    if a in ittenai:
        x,y=Nidxlst[a]
        main(x,y)
        ittenai.remove(a)
        value+=m

print(value)