#include <iostream>
#include <cmath>
#include <iomanip>
#include <vector>

using namespace std;

vector<int> x, y;

int dist2(int i, int j) {
    return (x[j] - x[i]) * (x[j] - x[i]) + (y[j] - y[i]) * (y[j] - y[i]);
}

int main() {
    freopen("unionday.in", "r", stdin);
    freopen("unionday.out", "w", stdout);

    int n;
    cin >> n;

    x.resize(static_cast<unsigned int>(n));
    y.resize(static_cast<unsigned int>(n));
    for (int i = 0; i < n; i++) {
        cin >> x[i] >> y[i];
    }

    double dist = 0;
    vector<int> used(n, 0), min_e(n, static_cast<const int &>(1e9)), end_e(n, -1);

    min_e[0] = 0;
    for (int i = 0; i < n; i++) {
        int v = -1;
        for (int j = 0; j < n; j++) {
            if (!used[j] && (v == -1 || min_e[j] < min_e[v])) {
                v = j;
            }
        }

        used[v] = 1;
        if (end_e[v] != -1) {
            dist += sqrt((double) dist2(v, end_e[v]));
        }

        for (int to = 0; to < n; to++) {
            int next_dist = dist2(v, to);
            if (!used[to] && next_dist < min_e[to]) {
                min_e[to] = next_dist;
                end_e[to] = v;
            }
        }
    }

    cout << fixed << setprecision(5) << dist << '\n';
    return 0;

}