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

double dis(double x1, double y1, double z1, double x2, double y2, double z2) {
  return sqrt(pow(x1-x2, 2) + pow(y1-y2, 2) + pow(z1-z2, 2));
}

int main() {
  int n;
  double xa[50010], ya[50010], za[50010];
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> xa[i] >> ya[i] >> za[i];
  }
  bool isSuc = true;
  do {
    for (int i = 0; i < n - 1; i++) {
      if(za[i] > za[i+1]) {
        swap(xa[i], xa[i+1]);
        swap(ya[i], ya[i+1]);
        swap(za[i], za[i+1]);
        isSuc = false;
      }
    }
  } while (isSuc = false);
  double ans = 0;
  for (int i = 0; i < n - 1; i++) {
    ans += dis(xa[i], ya[i], za[i], xa[i+1], ya[i+1], za[i+1]);
  }
  cout << fixed << setprecision(3) << ans << endl;
  return 0;
}