C++ :

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>
#include<algorithm>
#include<iostream>
using namespace std;
int parent[105];
struct lu
{
	int a,b;
	double length;
}lu[10010];

struct point
{
	double x,y;
	int num;
}point[105];

int root(int p)
{
	if(parent[p]==-1)
		return p;
	else return parent[p]=root(parent[p]);
}

void merge(int a,int b)
{
	a=root(a);
	b=root(b);
	parent[a]=b;
}

int cmp(const void *a,const void *b)
{
	struct lu *c,*d;
	c=(struct lu *)a;
	d=(struct lu *)b;
	if(c->length>d->length) return 1;
	if(c->length==d->length) return 0;
	if(c->length<d->length) return -1;
}

void ling()
{
	int i,j,k;
	for(i=0;i<105;i++)
		parent[i]=-1;
	for(i=0;i<10010;i++)
	{
		lu[i].length=0.0;
	}
}

int main()
{
	//freopen("B题测试数据.txt","r",stdin);
	//freopen("B题输出结果.txt","w",stdout);
	int i,j,k,l,m,n;
	double ans;
	while(scanf("%d",&n)!=EOF)
	{
		ling();
		for(i=0;i<n;i++)
		{
			scanf("%lf%lf",&point[i].x,&point[i].y);
		}
		l=0;
		ans=0.0;
		for(i=0;i<n;i++)
			for(j=i+1;j<n;j++)
			{
				lu[l].a=i;
				lu[l].b=j;
				lu[l].length=sqrt((point[i].x-point[j].x)*(point[i].x-point[j].x)+(point[i].y-point[j].y)*(point[i].y-point[j].y));
				l++;
			}
		qsort(lu,l,sizeof(struct lu),cmp);
		for(i=0;i<n*n;i++)
		{
			if(root(lu[i].a)!=root(lu[i].b))
			{
				merge(lu[i].a,lu[i].b);
				ans=ans+lu[i].length;
			}
		}
		printf("%.2lf\n",ans);
	}
	return 0;
}