#include <bits/stdc++.h>

using namespace std;
typedef long double ld;
const unsigned int INF = 1e8;
struct tt
{
    int x, y;
};
#define sqr(a) pow(a, 2)

int main()
{
    unsigned int n;
    cin >> n;
    vector <tt> a(n);
    vector<vector <unsigned int> > g(n);
    for (int i = 0; i < n; i++)
        cin >> a[i].x >> a[i].y;
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
        {
            if (i != j)
                g[i].push_back(sqr(a[i].x - a[j].x) + sqr(a[i].y - a[j].y));
            else
                g[i].push_back(INF);
        }
    vector<bool> used (n, false);
vector<int> min_e (n, INF), sel_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] = true;

	for (int to=0; to<n; ++to)
		if (g[v][to] < min_e[to] && !used[to]) { //2
			min_e[to] = g[v][to];
			sel_e[to] = v;
		}
}
    ld ans = 0;
    for (int i = 1; i < n; i++)
    {
        //cout << a[i].x << " " << a[i].y << " " << a[sel_e[i]].x << " " << a[sel_e[i]].y << endl;
        ans += sqrt(sqr(a[i].x - a[sel_e[i]].x) + sqr(a[i].y - a[sel_e[i]].y));
    }
    cout << setprecision(7) << fixed << ans << endl;
    return 0;
}