#include <iostream>
#include <vector>
#include <set>
#include <queue>
#include <algorithm>
#include <climits>
#include <cstdio>
#include <cassert>
#include <complex>
using namespace std;

#pragma optimize("",off)

#define for if(0);else for

typedef complex<double> pt;
struct cedge {
  int v1, v2;
  double c;
  cedge() {}
  cedge(int v1, int v2, double c) : v1(v1), v2(v2), c(c) {}
};

inline bool operator < (const cedge& a, const cedge& b)
{
  return a.c > b.c;
}

static inline
void AddVert(const vector<pt>& points,
             vector<bool>& S, priority_queue<cedge>& Q, int v)
{
  S[v] = true;
  for(int i = 0; i < points.size(); i++) {
    if(!S[i])
      Q.push(cedge(v, i, abs(points[i] - points[v])));
  }
}

double solve(const vector<pt>& points)
{
  if(points.empty()) return 0;
  
  vector<bool> S(points.size(), false);
  int size = 0;
  double total = 0;
  priority_queue<cedge> Q;
  AddVert(points, S, Q, 0), size++;
  //cout << "hoge" << endl;
  while(size < points.size()) {
    cedge c = Q.top(); Q.pop();
    if(S[c.v2]) continue;
    total += c.c;
    AddVert(points, S, Q, c.v2), size++;
  }
  return total;
}

int main()
{
  int N; cin >> N;
  vector<pt> points;
  while(N--) {
    double x, y; cin >> x >> y;
    points.push_back(pt(x, y));
  }
  
  double len = solve(points);
  char buffer[32];
  sprintf(buffer, "%.3f", len);
  cout << buffer << endl;
  
  return 0;
}