#include<iostream>
#include<string>
#include<algorithm>
#include<iomanip>
#include<math.h>
using namespace std;
struct h
{
	int x;
	int y;
	int z;
};
bool cmp(h x,h y)
{
	return x.z<y.z;
} 

int main()
{
	int t,v;
	cin>>t;
	struct h a[t];
	for(int i=0;i<t;i++)
	{
		cin>>a[i].x>>a[i].y>>a[i].z;
	}
    sort(a,a+t,cmp);
    double total=0;
	for(int i=1;i<t;i++)
		total+=sqrt((a[i-1].x-a[i].x)*(a[i-1].x-a[i].x)+(a[i-1].y-a[i].y)*(a[i-1].y-a[i].y)+(a[i-1].z-a[i].z)*(a[i-1].z-a[i].z));
	cout<<setprecision(4)<<total;
	return 0;
}