/*********************************
* 日期：2011-3-8
* 作者：SJF
* 题号：杭电1162
* 题目：Eddy's picture
* 结果：AC
* 总结：
**********************************/
#include <stdio.h>
#include <string.h>
#include <math.h>
int n;
double distance[101][101];
typedef struct
{
double x;
double y;
int visit;
}Point;
Point point[101];
void Distance()
{
int i,j,snum=1;//s[snum]表示已找出点的编号,snum找出点的个数
int s[101],minnum;
double min,len=0;
s[0]=0;
point[0].visit=1;
while(snum!=n+1)
{
min=0;
for(i=0;i<snum;i++)
{
for(j=0;j<n;j++)
{
if(point[j].visit==0)//该点没找过
{
if(distance[s[i]][j]<min||min==0)
{
min=distance[s[i]][j];
minnum=j;
}
}
}
}
s[snum]=minnum;
point[minnum].visit=1;
snum++;
len+=min;
}
printf("%.2lf\n",len);
}
int main()
{
int i,j;
double k;
while(scanf("%d",&n)!=EOF)
{
for(i=0;i<n;i++)
{
scanf("%lf %lf",&point[i].x,&point[i].y);
point[i].visit=0;
}
memset(distance,0,sizeof(distance));
for(i=0;i<n;i++)
{
for(j=i+1;j<n;j++)
{
k=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));
distance[j][i]=k;
distance[i][j]=k;
}
}
Distance();
}
return 0;
}