# Original solution
import sys
input = sys.stdin.readline
def INT(): return int(eval(input()))
def MAP(): return list(map(int,input().split()))
def LI(): return list(map(int,input().split()))
import decimal
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())

def main():
    N = INT()
    x = []
    y = []
    for _ in range(N):
        xx,yy = MAP()
        x.append(xx)
        y.append(yy)
    x = [(x[i],i) for i in range(N)]
    y = [(y[i],i) for i in range(N)]
    x.sort()
    y.sort()
    edges = []
    for i in range(N-1):
        edges.append((x[i][1],x[i+1][1],x[i+1][0]-x[i][0]))
        edges.append((y[i][1],y[i+1][1],y[i+1][0]-y[i][0]))
    edges.sort(key=lambda x:x[2])
    uf = UnionFind(N)
    answer = 0
    for i in range(len(edges)):
        s,t,w = edges[i]
        if not uf.same(s,t):
            uf.union(s,t)
            answer += w
    print(answer)
    return

if __name__ == '__main__':
    main()


# Optimized solution
import sys
input = sys.stdin.readline
def INT(): return int(eval(input()))
def MAP(): return list(map(int,input().split()))
def LI(): return list(map(int,input().split()))
import decimal
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())

def main():
    N = INT()
    x = []
    y = []
    for _ in range(N):
        xx,yy = MAP()
        x.append(xx)
        y.append(yy)
    x = [(x[i],i) for i in range(N)]
    y = [(y[i],i) for i in range(N)]
    x.sort(key=lambda x:x[0])
    y.sort(key=lambda x:x[0])
    edges = []
    for i in range(N-1):
        edges.append((x[i][1],x[i+1][1],x[i+1][0]-x[i][0]))
        edges.append((y[i][1],y[i+1][1],y[i+1][0]-y[i][0]))
    edges.sort(key=lambda x:x[2])
    uf = UnionFind(N)
    answer = 0
    for i in range(len(edges)):
        s,t,w = edges[i]
        if not uf.same(s,t):
            uf.union(s,t)
            answer += w
    print(answer)
    return

if __name__ == '__main__':
    main()