#include <iostream>
#include <algorithm>
#include <cmath>
#include <iomanip>
using namespace std;

int n;
struct post{
  int x;
  int y;
  int z;
}p[50005];
bool cmp(post a,post b){
    return a.z<b.z;
}
int main(){
    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-1;i++)
        ans+=sqrt((p[i].x-p[i+1].x)*(p[i].x-p[i+1].x)+(p[i].x-p[i+1].y)*(p[i].x-p[i+1].y)+(p[i].z-p[i+1].z)*(p[i].z-p[i+1].z));
    cout<<fixed<<setprecision(3)<<ans<<endl;
    return 0;
}

（话说这样例有点水