#include <math.h>
#include <iostream>
#include <vector>
using namespace std;

typedef long long ll;

struct pt
{
	ll x, y;
};

double dist(const pt& a, const pt& b)
{
	return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}

double g[5000][5000];
int chosenV[5000];
double minD[5000];
char used[5000];

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.setf(cout.fixed);
	cout.precision(12);

	int n;
	cin >> n;

	vector<pt> pts(n);

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

	for (int i = 0; i < n; i++)
	{
		for (int j = i + 1; j < n; j++)
		{
			g[i][j] = g[j][i] = dist(pts[i], pts[j]);
		}
	}

	fill(chosenV, chosenV + n, -1);
	fill(minD, minD + n, INF);

	minD[0] = 0;
	double res = 0;

	for (int i = 0; i < n; i++)
	{
		int v = -1;

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

		used[v] = 1;

		if (chosenV[v] != -1)
			res += g[v][chosenV[v]];

		for (int j = 0; j < n; j++)
		{
			if (minD[j] > g[v][j])
			{
				minD[j] = g[v][j];
				chosenV[j] = v;
			}
		}
	}

	cout << res;

	return 0;
}