package fgfgfgfgfgfgf;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class KruskullPrim {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        Coord[] c = new Coord[n];
        for (int i = 0; i<n; i++){
            c[i] = new Coord(in.nextDouble(), in.nextDouble(), i);
        }
        ArrayList<Edge> e = new ArrayList<Edge>();
        for (int i = 0; i<n-1; i++){ //O(n^2)
            for (int j = i+1; j<n; j++){
                e.add(new Edge(getDistance(c[i], c[j]), i, j));
            }
        }
        Collections.sort(e); //O(n^2*log(n^2))
        double res = 0;
        int tc = 0;
        for (int i = 0; i<e.size(); i++){ //O(n^2)
            if (c[e.get(i).v1].color!=c[e.get(i).v2].color){
                c[e.get(i).v2].color = c[e.get(i).v1].color;
                res+=e.get(i).weight;
                tc++;
            }
            if (tc==n-1) break;
        }
        System.out.println(res);
    }
    public static double getDistance(Coord p1, Coord p2){
        return Math.sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
    }

}
class Coord{
    double x;
    double y;
    int color;
    public Coord(double x, double y, int color){
        this.x = x;
        this.y = y;
        this.color = color;
    }
}
class Edge implements Comparable<Edge>{
    double weight;
    int v1;
    int v2;
    public Edge(double weight, int v1, int v2){
        this.weight = weight;
        this.v1 = v1;
        this.v2 = v2;
    }
    @Override
    public int compareTo(Edge e) {
        return Double.compare(this.weight, e.weight);
    }
}