#include <iostream>
#include <algorithm>
#include <cmath>
#include <iomanip>

using namespace std;

const int N = 100010;

int n;
double ans;

struct S {
	int x, y, z;
	bool operator<(const S& a)const {
		return z < a.z;
	}
}a[N];

int main() {
	cin >> n;
	for (int i = 0; i < n; cin >> a[i].x >> a[i].y >> a[i++].z);
	sort(a, a + n);
	for (int i = 1, j = 0; i < n; ++j, ++i) {
		ans += sqrt(pow(a[i].x - a[j].x, 2) + pow(a[i].y - a[j].y, 2) + pow(a[i].z - a[j].z, 2));
	}
	cout << fixed << setprecision(3) << ans << endl;
	return 0;
}

样例输出： 16.103%25V%607_Q97.png)