#include<iostream>
#include<algorithm>
#include<cmath>
#include<iomanip>
using namespace std;
int main()
{
	int n, x[50005], y[50005], z[50005];
	double a[50005] = { 0 }, sum = 0;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> x[i]>>y[i]>>z[i];
	}
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < n - i - 1; j++)
		{
			if (z[i] > z[i + 1])
			{
				int z1 = z[i];
				z[i] = z[i + 1];
				z[i + 1] = z1;
				int x1 = x[i];
				x[i] = x[i + 1];
				x[i + 1] = x1;
				int y1 = y[i];
				y[i] = y[i + 1];
				y[i + 1] = y1;
			}
			
		}
	}
	for (int i = 0; i < n-1; i++)
	{
		a[i] = sqrt((x[i + 1] - x[i]) * (x[i + 1] - x[i]) + (y[i + 1] - y[i]) * (y[i + 1] - y[i]) + (z[i + 1] - z[i]) * (z[i + 1] - z[i]));
		sum += a[i];
	}
	cout << setiosflags(ios::fixed) << setprecision(3) << sum;
	return 0;
}