#include"iostream"
#include"algorithm"
#include"cmath"
using namespace std;
const int N = 1024;
struct point
{
	int x, y, z;
}a[N];
bool cmp(point a, point b)
{
	return a.z < b.z;
}
int main()
{
	int n;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> a[i].x >> a[i].y >> a[i].z;
	}
	sort(a, a + n, cmp);
	double path=0;
	for (int i = 0; i < n-1; i++)
	{
		path += 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));
	}
	printf("%.3lf", path);
	return 0;
}