# include <iostream>
# include <algorithm>
# include <math.h>

using namespace std;

typedef struct
{
	int x;
	int y;
	int z;
 } point;
 
 bool cmp(point a, point b)
 {
 	if(a.x != b.x)
 	  return a.x < b.x;
 	else 
 	{
 		if(a.y != b.y)
 		  return a.y < b.y;
 		else
 		{
 			if(a.z != b.z)
 			{
 				return a.z < b.z;
			 }
		 }
	 }
 }
 
 int main()
 {
 	int n,i;
 	point p[50001];
 	scanf("%d",&n);
 	for(i = 0; i < n; i++)
 	{
 		scanf("%d%d%d",&p[i].x,&p[i].y,&p[i].z);
	 }
	 sort(p,p + n,cmp);
	 double len;
	 for(i = 0; i < n-1; i++)
	 {
	 	len += sqrt((p[i+1].x - p[i].x)*(p[i+1].x - p[i].x) + (p[i+1].y - p[i].y)*(p[i+1].y - p[i].y) + (p[i+1].z - p[i].z)*(p[i+1].z - p[i].z));
	  } 
	  printf("%.3lf\n",len);
 	return 0;
 }