# Original solution
# ユニオンファインド
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(eval(input()))
a= [list(map(int, input().split())) for i in range(n)]
b=[]
a.sort()
# aの各点に通し番号を振る
for i in range(n):
    a[i].append(i)

# 繋ぐ点の候補は上下左右の４つ
# 左右に繋ぐ辺を追加
for i in range(n):
    if i==0:
        b.append([a[i][2],a[i+1][2], a[i+1][0]-a[i][0]])
    elif i==n-1:
        b.append([a[i][2],a[i-1][2], a[i][0]-a[i-1][0]])
    else:
        b.append([a[i][2],a[i-1][2], a[i][0]-a[i-1][0]])
        b.append([a[i][2], a[i + 1][2], a[i + 1][0] - a[i][0]])

a.sort(key=lambda x:x[1])
# 上下に繋ぐ辺を追加
for i in range(n):
    if i==0:
        b.append([a[i][2],a[i+1][2], a[i+1][1]-a[i][1]])
    elif i==n-1:
        b.append([a[i][2],a[i-1][2], a[i][1]-a[i-1][1]])
    else:
        b.append([a[i][2],a[i-1][2], a[i][1]-a[i-1][1]])
        b.append([a[i][2], a[i + 1][2], a[i + 1][1] - a[i][1]])

b.sort(key=lambda x:x[2])

uf=UnionFind(n)
ans=0
cnt=0
# クラスカル法
for x,y,z in b:
    if not uf.same(x,y):
        uf.union(x,y)
        cnt+=1
        ans+=z
        if cnt==n-1:
            break
print(ans)

# Optimized solution
# ユニオンファインド
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(eval(input()))
a= [list(map(int, input().split())) for i in range(n)]
b=[]
a.sort()
# aの各点に通し番号を振る
for i in range(n):
    a[i].append(i)

# 繋ぐ点の候補は上下左右の４つ
# 左右に繋ぐ辺を追加
for i in range(n-1):
    b.append([a[i][2], a[i + 1][2], a[i + 1][0] - a[i][0]])

a.sort(key=lambda x:x[1])
# 上下に繋ぐ辺を追加
for i in range(n-1):
    b.append([a[i][2], a[i + 1][2], a[i + 1][1] - a[i][1]])

b.sort(key=lambda x:x[2])

uf=UnionFind(n)
ans=0
cnt=0
# クラスカル法
for x,y,z in b:
    if not uf.same(x,y):
        uf.union(x,y)
        cnt+=1
        ans+=z
        if cnt==n-1:
            break
print(ans)