rt

#include<bits/stdc++.h>
#define MAXN 100000000
using namespace std;
double ans;
struct zuob{
	double x;
	double y;
	double z;
}n[50002];
bool cmp(zuob a,zuob b){
	return a.z<b.z;
}
double sq(double x){
	return x*x;
}
double l(double x1,double x2,double y1,double y2,double z1,double z2){
	return sqrt(sq(abs(x1-x2))+sq(abs(y1-y2))+sq(abs(z1-z2)));
}
int main(){
	int a;
	cin>>a;
	for(int i=0;i<a;i++){
		cin>>n[i].x>>n[i].y>>n[i].z;
	}
	sort(n,n+a+1,cmp);
	for(int i=0;i<a-1;i++){
	 ans+=l(n[i].x,n[i+1].x,n[i].y,n[i+1].y,n[i].z,n[i+1].z);	
	}
	printf("%.3lf",ans);
}