#include<bits/stdc++.h>
using namespace std;
long long n;
double s,stt;
struct st{
	long long x,y,z;
}a[50005];
bool cmp(st a,st b){
	return a.x<b.x;
}
//double f(double a,double b,double c,double d,double e,double sf){
//	return sqrt(pow(a-b,2)+pow(c-d,2)+pow(e-sf,2));
//} 
int main()
{
	cin>>n;
	for(int i=1;i<=n;i++)
		cin>>a[i].x>>a[i].y>>a[i].z;
	sort(a+1,a+n+1,cmp);
	for(int i=2;i<=n;i++)	
	{
//		s+=f(a[i-1].x,a[i].x,a[i-1].y,a[i].y,a[i-1].z,a[i].z);
//		s+=sqrt(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));
		s+=sqrt((a[i-1].x-a[i].x)*(a[i-1].x-a[i].x)+(a[i-1].y-a[i].y)*(a[i-1].y-a[i].y)+(a[i-1].z-a[i].z)*(a[i-1].z-a[i].z));
	}
	printf("%.3lf\n",s);
	return 0;
}