n=int(input())
l=sorted([list(map(int,input().split()))+[i] for i in range(n)])
xs=[(x,i)for x,y,i in l]
ys=sorted([(x,i)for y,x,i in l])
edges={}
for i in range(1,n):
    a,s,d,f=*xs[i-1],*xs[i]
    if (s,f)in edges:
        edges[(s,f)]=min(edges[(s,f)],abs(a-d))
    else:edges[(s,f)]=abs(a-d)
    a,s,d,f=*ys[i-1],*ys[i]
    if (s,f)in edges:
        edges[(s,f)]=min(edges[(s,f)],abs(a-d))
    else:edges[(s,f)]=abs(a-d)
edges=sorted(edges.items(),key=lambda x:x[1])
class UnionFind:
    #def   -> foo=UnionFind(n,1)  <- 1-based index, default is 0
    #method -> foo.hoge(huga)
    __slots__ = ["_size", "_first_idx", "_parents"]
    def __init__(self, size: int, first_index: int = 0) -> None:
        self._size = size
        self._first_idx = first_index
        self._parents = [-1] * (size + first_index)
    def find(self, x: int) -> int:
        if self._parents[x] < 0:
            return x
        self._parents[x] = self.find(self._parents[x])
        return self._parents[x]
    def same(self, x: int, y: int) -> bool:
        return self.find(x) == self.find(y)
    def unite(self, x: int, y: int) -> bool:
        x, y = self.find(x), self.find(y)
        if x == y:
            return False
        if self._parents[x] > self._parents[y]:
            x, y = y, x
        self._parents[x] += self._parents[y]
        self._parents[y] = x
        return True
    def size(self, x: int) -> int:
        return -self._parents[self.find(x)]
    def group_count(self) ->int:
        return sum(1 for i in  self._parents if i<0)-self._first_idx
    def connected(self) ->bool:
        return self._parents[self.find(self._first_idx)]==-self._size
uf=UnionFind(n)
ans=edges[0][1]
uf.unite(*edges[0][0])
for f,c in edges:
    if uf.same(*f):continue
    uf.unite(*f)
    ans+=c
print(ans)

### FIXED CODE ###

n=int(input())
l=sorted([list(map(int,input().split()))+[i] for i in range(n)])
xs=[(x,i)for x,y,i in l]
ys=sorted([(x,i)for y,x,i in l])
edges={}
for i in range(1,n):
    a,s=xs[i-1];d,f=xs[i]
    if (s,f)in edges:
        edges[(s,f)]=min(edges[(s,f)],abs(a-d))
    else:edges[(s,f)]=abs(a-d)
    a,s=ys[i-1];d,f=ys[i]
    if (s,f)in edges:
        edges[(s,f)]=min(edges[(s,f)],abs(a-d))
    else:edges[(s,f)]=abs(a-d)
edges=sorted(edges.items(),key=lambda x:x[1])
class UnionFind:
    #def   -> foo=UnionFind(n,1)  <- 1-based index, default is 0
    #method -> foo.hoge(huga)
    __slots__ = ["_size", "_first_idx", "_parents"]
    def __init__(self, size: int, first_index: int = 0) -> None:
        self._size = size
        self._first_idx = first_index
        self._parents = [-1] * (size + first_index)
    def find(self, x: int) -> int:
        if self._parents[x] < 0:
            return x
        self._parents[x] = self.find(self._parents[x])
        return self._parents[x]
    def same(self, x: int, y: int) -> bool:
        return self.find(x) == self.find(y)
    def unite(self, x: int, y: int) -> bool:
        x, y = self.find(x), self.find(y)
        if x == y:
            return False
        if self._parents[x] > self._parents[y]:
            x, y = y, x
        self._parents[x] += self._parents[y]
        self._parents[y] = x
        return True
    def size(self, x: int) -> int:
        return -self._parents[self.find(x)]
    def group_count(self) ->int:
        return sum(1 for i in  self._parents if i<0)-self._first_idx
    def connected(self) ->bool:
        return self._parents[self.find(self._first_idx)]==-self._size
uf=UnionFind(n)
ans=edges[0][1]
uf.unite(*edges[0][0])
for f,c in edges:
    if uf.same(*f):continue
    uf.unite(*f)
    ans+=c
print(ans)