import java.util.Scanner;
import java.lang.Math;

class Point{
    int x,y;
}
class Edge{
    double l;
    int x,y;
}
class KTree{
    int parent,rank;
}

public class Kruskal {
    //static Edge e;
    static Edge[] E;
    static Point[] P;
    static  KTree[] T;
    static int length;
    public static void union(int a,int b){
        int c;
        if (T[a].rank > T[b].rank){
            c = a;
            a = b;
            b = c;
        }
        else if (T[a].rank != T[b].rank){
            T[a].parent = b;
        }
        else if (T[a].rank == T[b].rank) {
            T[b].rank++;
        }
        T[a].parent = b;
    }
    public static int find(int a){
        if (a == T[a].parent) {
            return a;
        }
        return T[a].parent = find(T[a].parent);
    }
    public static void heapify(int a) {
        int i;
        i = a;
        Edge c;
        if (2*a<length) {
            if (E[a].l>E[2*a].l) {
                i=2*a;
            }
        }
        if (2*a+1<length) {
            if (E[i].l>E[a*2+1].l) {
                i=2*a+1;
            }
        }
        if (i>a) {
            c=E[i];
            E[i]=E[a];
            E[a]=c;
            a=i;
            heapify(a);
        }
       // System.out.println("!!!");
    }
    public static void delete(){
        E[0]=E[length-1];
        length--;
        heapify(0);
       // System.out.println("!");
    }
    public static double SpanningTree(int n){
        int i,k;
        double sum=0.0;
        for (i=length/2; i>=0; i--) {
            heapify(i);
        }
       // System.out.println("!!");
        for (k=0;k!=n-1;) {
            if (find(E[0].x)!=find(E[0].y)) {
                union(find(E[0].x),find(E[0].y));
                sum += E[0].l;
                k++;
            }
            delete();
        }
        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int i,j;
        //Edge e=new Edge();
        P = new Point[n];
        E = new Edge[(n*n-n)/2];
        T = new KTree[n];
        length=(n*n-n)/2;
        int k=0;
        double sumMin;
        for (i=0;i<n;i++) {
            T[i]=new KTree();
            P[i]=new Point();
            T[i].parent = i;
            P[i].x=in.nextInt() ;
            P[i].y=in.nextInt() ;
            for (j=i-1;j>=0;j--) {
                Edge e=new Edge();
                e.l = Math.sqrt(((double)(P[i].x-P[j].x)*(P[i].x-P[j].x)+(P[i].y-P[j].y)*(P[i].y-P[j].y)));
                e.x=j;
                e.y=i;
                E[k] = e;
                k++;
            }
        }
        sumMin=SpanningTree(n);
        System.out.printf("%.2f",sumMin);
    }
}