#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
struct point{
	int x,y,z;
}; 
bool cmp(point b,point c){
    return b.z<c.z;
}
int main(){
	int n;
	double ans=0;
	scanf("%d",&n);
	point points[50001];
	for(int i=0;i<n;i++)scanf("%d%d%d",&points[i].x,&points[i].y,&points[i].z);
	sort(points,points+n,cmp);
	for(int i=1;i<n;i++)ans+=sqrt((points[i].x-points[i-1].x)*(points[i].x-points[i-1].x
	                             +(points[i].y-points[i-1].y)*(points[i].y-points[i-1].y
	                             +(points[i].z-points[i-1].z)*(points[i].z-points[i-1].z))));
    printf("%.3lf",ans);
	return 0;
}