#include <iostream>
#include <bits/stdc++.h>

using namespace std;

const int INF = 1e9;

int main()
{
    freopen("unionday.in", "r", stdin);
    freopen("unionday.out", "w", stdout);
    int n; cin >> n;
    double g[n][n];

    //g.resize(n);

    //for (int i = 0;i < n; i++) g[i].resize(n);

    vector <pair <int, int> > point(n);

    for (int i = 0; i < n; i++){
        int x,y; scanf("%d %d", &x, &y);
        point[i] = make_pair(x, y);
    }

    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            double cost = ((point[i].first - point[j].first)*(point[i].first - point[j].first) + (point[i].second - point[j].second) * (point[i].second - point[j].second));
            g[i][j] = cost;
            g[j][i] = cost;
        }
    }

    vector <bool> used(n);
    vector <int> min_edge(n, INF), end_edge(n, -1);
    min_edge[0] = 0;

    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_edge[j] < min_edge[v]))
                v = j;


        used[v] = 1;

        if (end_edge[v] != -1) ans += sqrtl(g[v][end_edge[v]]);

        for (int to = 0; to < n; to++)
            if (g[v][to] < min_edge[to]){
                min_edge[to] = g[v][to];
                end_edge[to] = v;
        }
    }

    printf("%f", ans);

    return 0;
}