#include <fstream>
#include <queue>
#include <cmath>
#include <iomanip>

using namespace std;

ifstream f("cablaj.in");
ofstream g("cablaj.out");

#define NMAX 3005

int n;
bool viz[NMAX];
double sol, dist_min[NMAX];
pair<int, int> localitati[NMAX];
priority_queue<pair<double, int>, vector<pair<double, int>>, greater<>> q;

void citire() {
    f >> n;
    for (int i = 1; i <= n; ++i)
        f >> localitati[i].first >> localitati[i].second;
}

double distanta(int x, int y) {
    return sqrt((double) (localitati[x].first - localitati[y].first) * (localitati[x].first - localitati[y].first) +
                (localitati[x].second - localitati[y].second) * (localitati[x].second - localitati[y].second));
}

void initializare() {
    dist_min[1] = 0;
    viz[1] = true;
    for (int i = 2; i <= n; i++) {
        dist_min[i] = distanta(1, i);
        q.push({dist_min[i], i});
    }
}

void actualizare_distante(int nod) {
    for (int i = 2; i <= n; i++)
        if (!viz[i])
            if (distanta(nod, i) < dist_min[i]) {
                dist_min[i] = distanta(nod, i);
                q.push({dist_min[i], i});
            }
}

void prelucrare() {
    while (!q.empty()) {
        pair<double, int> muchie = q.top();
        q.pop();
        if (viz[muchie.second])
            continue;
        viz[muchie.second] = true;
        sol += muchie.first;
        actualizare_distante(muchie.second);
    }
}

int main() {
    citire();
    initializare();
    prelucrare();
    g << fixed << setprecision(3) << sol;
    return 0;
}