#include <cmath>
#include <iomanip>
#include <algorithm>
#include <iostream>
using namespace std;
int n;
double sum;
struct point{
    double x, y, z;
};
bool cmp(point a, point b){
    return a.z < b.z;
}
int main(){
    point po[50010];
    cin >> n;
    for(int i = 0; i < n; i++){
        cin >> po[i].x >> po[i].y >> po[i].z;
    }sort(po, po + n, cmp);
    for(int i = 0; i < n - 1; i++){
        sum += sqrt(pow(po[i].x - po[i - 1].x, 2) + pow(po[i].y - po[i - 1].y, 2) + pow(po[i].z - po[i - 1].z, 2));
    }cout << fixed << setprecision(3) << sum << endl;
    return 0;
}