#include<iostream>
#include<cmath>
#include<algorithm>
#include<vector>
#include<cstdio>
using namespace std;
#define re register
inline double POW(int a){
	return a * a * 1.0;
}
class Cooridinate {
public:
	int x;
	int y;
	int z;
	Cooridinate():x(0),y(0),z(0){}
};
inline double distance(Cooridinate& a, Cooridinate& b);
bool cmp(Cooridinate& a,Cooridinate& b) {
	return a.z < b.z;
}
int main(void) 
{
	int N;//N个点
	cin >> N;
	vector<Cooridinate> cod(N);
	for (re int i = 0; i < N; i++)
		cin >> cod[i].x >> cod[i].y >> cod[i].z;
	sort(cod.begin(),cod.end(),cmp);
	double ans = 0;
	for (re int i = 0; i < N-1; i++)
		ans += distance(cod[i], cod[i + 1]);
	printf("%.3f\n", ans);
	return 0;
}
inline double distance(Cooridinate& a, Cooridinate& b) {
	return sqrt(POW(a.x - b.x) + POW(a.y - b.y) + POW(a.z - b.z));
}