#include<bits/stdc++.h>
using namespace std;
struct pashang{
	double x;
	double y;
	double z;
}a[1000001];
double dis(double x1,double y1,double z1,double x2,double y2,double z2)
{
	double c=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)+(z1-z2)*(z1-z2));
	return c;
}
bool cmp(pashang o,pashang p)
{
	return o.z<p.z;
}
int main()
{
	int n,i,j;
	cin>>n;
	for(i=1;i<=n;i++)
	{
		cin>>a[i].x>>a[i].y>>a[i].z;
	}
	sort(a+1,a+n+1,cmp);
	double s=0;
	for(i=1;i<n;i++)
	{
		s+=dis(a[i].x,a[i].y,a[i].z,a[i+1].x,a[i+1].y,a[i+1].z);
	}
	cout<<fixed<<setprecision(3)<<s;
}