#include<bits/stdc++.h>
using namespace std;
struct sd{
	double x,y,z;
}p[10000]; 
bool cmp(sd a,sd b){
	if(a.x>b.x)return false;
	if(a.y>b.y)return false;
	if(a.z>b.z)return false;
	return true;
}
int main(){
	int n;
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>p[i].x>>p[i].y>>p[i].z;
	} 
	sort(p+1,p+n+1,cmp);
	double ans=0;
	for(int i=1;i<n;i++){
		ans+=sqrt((p[i+1].x-p[i].x)*(p[i+1].x-p[i].x)+(p[i+1].y-p[i].y)*(p[i+1].y-p[i].y)+(p[i+1].z-p[i].z)*(p[i+1].z-p[i].z));
	}
	printf("%.3lf",ans);
	return 0;
}