#include<iostream>
#include<stdio.h>
#include<math.h>
using namespace std;
int main()
{
	int n,i,j,k,x[100]={0},y[100]={0},z[100]={0},tz,l,tx,ty;
	double range=0,distance=0;
	cin>>n;
	for(i=0;i<n;i++)
	{
		cin>>x[i]>>y[i]>>z[i];
	}
	for(l=1;l<n-1;l++)
	{
		for(j=1;j<n-1;j++)
		{
			if(z[j]>z[j+1])
		    {
			tz=z[j];tx=x[j];ty=y[j];
		    z[j]=z[j+1];x[j]=x[j+1];y[j]=y[j+1];
		    z[j+1]=tz;x[j+1]=tx;y[j+1]=ty;
		    }
		}
	} 
		for(k=1;k<n-1;k++)
		{
			distance=sqrt(pow(x[k]-x[k+1],2)+pow(y[k]-y[k+1],2)+pow(z[k]-z[k+1],2));
			range=distance+range;
		}
		printf("%.3f",range);
}