#[allow(unused_imports)]
use std::cmp::*;
#[allow(unused_imports)]
use std::collections::*;

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        eprintln!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
    }
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

#[derive(Debug, Clone)]
struct Edge {
    from: usize,
    to: usize,
    cost: u64,
}

impl PartialEq for Edge {
    fn eq(&self, other: &Edge) -> bool {
        self.cost == other.cost
    }
}

impl Eq for Edge {}

impl Ord for Edge {
    fn cmp(&self, other: &Self) -> Ordering {
        self.cost.cmp(&other.cost)
    }
}

impl PartialOrd for Edge {
    fn partial_cmp(&self, other: &Edge) -> Option<Ordering> {
        Some(self.cost.cmp(&other.cost))
    }
}

struct UnionFindTree {
    parent_or_size: Vec<isize>,
}

impl UnionFindTree {
    fn new(size: usize) -> UnionFindTree {
        UnionFindTree {
            parent_or_size: vec![-1; size],
        }
    }

    fn find(&self, index: usize) -> usize {
        let mut index = index;
        while self.parent_or_size[index] >= 0 {
            index = self.parent_or_size[index] as usize;
        }
        index
    }

    fn same(&self, x: usize, y: usize) -> bool {
        self.find(x) == self.find(y)
    }

    fn unite(&mut self, index0: usize, index1: usize) -> bool {
        let a = self.find(index0);
        let b = self.find(index1);
        if a == b {
            false
        } else {
            if self.parent_or_size[a] < self.parent_or_size[b] {
                self.parent_or_size[a] += self.parent_or_size[b];
                self.parent_or_size[b] = a as isize;
            } else {
                self.parent_or_size[b] += self.parent_or_size[a];
                self.parent_or_size[a] = b as isize;
            }
            true
        }
    }
}

fn kruskal(edges: &Vec<Edge>, num_apexes: usize) -> u64 {
    let mut edges = edges.clone();
    let mut res = 0;
    edges.sort();
    let mut unf = UnionFindTree::new(num_apexes);
    for e in edges {
        if !unf.same(e.to, e.from) {
            debug!(e);
            unf.unite(e.to, e.from);
            res += e.cost;
        }
    }
    res
}

fn argsort<T: std::cmp::Ord + std::marker::Copy>(v: &Vec<T>) -> Vec<usize> {
    let mut sort_v = Vec::new();
    for i in 0..v.len() {
        sort_v.push((v[i], i));
    }
    sort_v.sort();
    sort_v.iter().map(|x| x.1).collect::<Vec<usize>>()
}

fn main() {
    let n = read::<usize>();
    let mut x = vec![0u64; n];
    let mut y = vec![0u64; n];
    for i in 0..n {
        let v = read_vec::<u64>();
        x[i] = v[0];
        y[i] = v[1];
    }
    let x_indexes = argsort(&x);
    let y_indexes = argsort(&y);

    let mut edges = Vec::new();
    for i in 1..n {
        let prev = x_indexes[i - 1];
        let next = x_indexes[i];
        let edge = Edge {
            from: next,
            to: prev,
            cost: x[next] - x[prev],
        };
        edges.push(edge);
    }
    for i in 1..n {
        let prev = y_indexes[i - 1];
        let next = y_indexes[i];
        let edge = Edge {
            from: next,
            to: prev,
            cost: y[next] - y[prev],
        };
        edges.push(edge);
    }
    debug!(edges);
    println!("{}", kruskal(&edges, n));
}
