#include<iostream>
#include<algorithm>
#include<cmath>
using namespace std;
struct p{
	int x;
	int y;
	int z;
};
bool tmp(p a,p b){
	return a.z<b.z;
}
int main(){
	int n;
	cin>>n;
	p a[n];
	for(int i=0;i<n;i++){
		cin>>a[i].x>>a[i].y>>a[i].z;
	}
	sort(a,a+n,tmp);
	double sum=0;
	for(int i=1;i<n;i++){
		sum+=sqrt(0.000+pow((a[i-1].x-a[i].x),2)+pow((a[i-1].y+a[i].y),2)+pow((a[i-1].z+a[i].z),2));
	}
	cout<<sum;
}