### BUGGY CODE ###

class UnionFindNode(object):
    """
    Union-Find構造
    ノードのグループ併合や、所属グループ判定を高速に処理する
    """

    def __init__(self, group_id, parent=None, value=None):
        self.group_id_ = group_id
        self.parent_ = parent
        self.value = value
        self.size_ = 1

    def __str__(self):
        template = "UnionFindNode(group_id: {}, \n\tparent: {}, value: {}, size: {})"
        return template.format(self.group_id_, self.parent_, self.value, self.size_)

    def is_root(self):
        return not self.parent_

    def root(self):
        parent = self
        while not parent.is_root():
            parent = parent.parent_
            self.parent_ = parent
        return parent

    def find(self):
        parent = self.root()
        return parent.group_id_

    def size(self):
        parent = self.root()
        return parent.size_

    def unite(self, unite_node):
        parent = self.root()
        unite_parent = unite_node.root()

        if parent.group_id_ != unite_parent.group_id_:
            if parent.size() > unite_parent.size():
                unite_parent.parent_ = parent
                parent.size_ = parent.size_ + unite_parent.size_
            else:
                parent.parent_ = unite_parent
                unite_parent.size_ = parent.size_ + unite_parent.size_
    def is_group(self,other):#selfとotherが同じグループに属するか
        return self.root()==other.root()


N=int(input())
X=[]
Y=[]
for i in range(N):
    x,y=map(int,input().split())
    X.append((x,i))
    Y.append((y,i))
X.sort()
Y.sort()
E=[]
ans=0
count=1
for i in range(N-1):
    a=X[i]
    b=X[i+1]
    c=Y[i]
    d=Y[i+1]
    E.extend([(b[0]-a[0],X[i][1],X[i+1][1]),(d[0]-c[0],Y[i][1],Y[i+1][1])])
E.sort()

U=[UnionFindNode(i) for i in range(N)]
for cost,v1,v2 in E:
    if not U[v1].is_group(U[v2]):
        U[v1].unite(U[v2])
        ans+=cost
        count+=1
    if count==N:
        break
print(ans)


### FIXED CODE ###

class UnionFind:
    def __init__(self, n):
        self.par = [i for i in range(n+1)]
        self.rank = [0] * (n+1)
        self.size = [1] * (n+1)

    # 検索
    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

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

        if x == y:
            return

        if self.rank[x] < self.rank[y]:
            self.par[x] = y
        else:
            self.par[y] = x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1

    # 同じ集合に属するか判定
    def same_check(self, x, y):
        return self.find(x) == self.find(y)
"""
N=int(input())
X=[]
Y=[]
for i in range(N):
    x,y=map(int,input().split())
    X.append((x,i))
    Y.append((y,i))
X.sort()
Y.sort()
E=[]
ans=0
count=1
for i in range(N-1):
    a=X[i]
    b=X[i+1]
    c=Y[i]
    d=Y[i+1]
    E.extend([(b[0]-a[0],X[i][1],X[i+1][1]),(d[0]-c[0],Y[i][1],Y[i+1][1])])
E.sort()
"""
N = int(input())
P = [[i, list(map(int, input().split()))] for i in range(N)]

X = sorted([[i, xy[0]] for i, xy in P], key=lambda x: x[1])
Y = sorted([[i, xy[1]] for i, xy in P], key=lambda y: y[1])

Xe = [[X[i][0], X[i+1][0], abs(X[i][1]-X[i+1][1])] for i in range(N-1)]
Ye = [[Y[i][0], Y[i+1][0], abs(Y[i][1]-Y[i+1][1])] for i in range(N-1)]
E = sorted(Xe + Ye, key=lambda e: e[2])
U=UnionFind(N)
i=0
ans=0
count=1
while(count<N):
    v1,v2,cost=E[i]
    if not U.same_check(v1,v2):
        U.union(v1,v2)
        ans+=cost
        count+=1
    i+=1
print(ans)