////  1144 Freckles.cpp//  Jobdu////  Created by PengFei_Zheng on 18/04/2017.//  Copyright © 2017 PengFei_Zheng. All rights reserved.// #include <stdio.h>#include <iostream>#include <algorithm>#include <string.h>#include <cmath>#define MAX_SIZE 110  using namespace std; int tree[MAX_SIZE]; int findRoot(int x){// find the root of x    if(tree[x] == -1) return x;    else{        int tmp = findRoot(tree[x]);        tree[x] = tmp;        return tmp;    }} struct Edge{// define the edge which have line  a and  line b    int a, b;    double cost; // the length of point a to point b    bool operator < (const Edge &A) const{        return cost < A.cost;    }};  struct Point{//define the point    double x, y;//(x,y) the position of this dot    double getDistance(Point A){//get the lenght between (x,y) and (A.x, A.y)        double tmp = (x-A.x)*(x-A.x) + (y-A.y)*(y-A.y);        return sqrt(tmp);    }}; int n; int main(){    while(scanf("%d",&n)!=EOF){                 Edge edge[n*(n-1)/2+1];        Point point[n+1];                 for(int i = 1 ; i <= n ; i++){            scanf("%lf%lf",&point[i].x,&point[i].y);//input the pos of (x,y)            tree[i]=-1;//init the node i        }        int line_id = 0;//define the id of the line        for(int i = 1 ; i <= n ; i++){            for(int j = i+1 ; j <= n ; j++){                edge[line_id].a = i;                edge[line_id].b = j;                edge[line_id].cost = point[i].getDistance(point[j]);//cal the length point[i] to point[y]                line_id++;            }        }                 sort(edge,edge+line_id);// from low to high                 double ans = 0;                 for(int i = 0 ; i < line_id ; i++){            int a = findRoot(edge[i].a);            int b = findRoot(edge[i].b);            if(a!=b){//merge the a node to b‘s aggregate                tree[a] = b;                ans += edge[i].cost;            }        }        printf("%.2lf\n",ans);    }    return 0;     }/**************************************************************    Problem: 1144    User: zpfbuaa    Language: C++    Result: Accepted    Time:10 ms    Memory:1520 kb****************************************************************/