#include<bits/stdc++.h>
using namespace std;
struct node{
	int x,y,z;
}d[5005];
bool cmp(node a,node 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;
	double ans=0;
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		cin>>d[i].x>>d[i].y>>d[i].z;
	}
	sort(d+1,d+n+1,cmp);
	for(int i=2;i<=n;i++){
		ans+=sqrt((d[i].x-d[i-1].x)*(d[i].x-d[i-1].x)+(d[i].y-d[i-1].y)*(d[i].y-d[i-1].y)+(d[i].z-d[i-1].z)*(d[i].z-d[i-1].z));
	}
	printf("%.3lf",ans);
	return 0;
}