#include <bits/stdc++.h>
using namespace std;

const int INF = int(1e9);
int n;
vector <int> x, y;
vector <vector <long double> > gr;
vector <bool> used;
vector <int> min_e, sel_e;

int main() {
    cin >> n;
    x.resize(n); y.resize(n);
    gr.resize(n, vector <long double> (n));
    min_e.assign(n, INF); sel_e.assign(n, -1);
    used.assign(n, 0);

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

    long double ans = 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;
        }
        if (sel_e[v] != -1)
            ans += sqrt((x[v] - x[sel_e[v]]) * (x[v] - x[sel_e[v]]) + (y[v] - y[sel_e[v]]) * (y[v] - y[sel_e[v]]));
        used[v] = true;
        for (int to = 0; to < n; to++) {
            if (sqrt((x[v] - x[to]) * (x[v] - x[to]) + (y[v] - y[to]) * (y[v] - y[to])) < min_e[to]) {
                min_e[to] = sqrt((x[v] - x[to]) * (x[v] - x[to]) + (y[v] - y[to]) * (y[v] - y[to]));
                sel_e[to] = v;
            }
        }
    }
    cout << fixed << setprecision(15) << ans;
    return 0;
}