import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Arrays;
import java.util.PriorityQueue;
import java.util.StringTokenizer;

public class Spantree implements Runnable {

	private String nextToken() {
		if (st == null || !st.hasMoreTokens()) {
			try {
				st = new StringTokenizer(in.readLine());
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		return st.nextToken();
	}

	private int nextInt() {
		return new Integer(nextToken());
	}

	private long nextLong() {
		return new Long(nextToken());
	}

	private class Pair implements Comparable<Pair> {
		public int v;
		public int d;

		public Pair(int v, int d) {
			this.v = v;
			this.d = d;
		}

		@Override
		public int compareTo(Pair o) {
			return this.d - o.d;
		}

	}

	private StringTokenizer st;
	private BufferedReader in;
	private BufferedWriter out;

	class Point implements Comparable<Point> {
		public double x;
		public double y;

		public double dist;
		public int num;

		public Point(int x, int y, int num) {
			super();
			this.x = x;
			this.y = y;
			this.num = num;
		}

		public Point(Point p, double dist) {
			this.x = p.x;
			this.y = p.y;
			this.num = p.num;
			this.dist = dist;
		}

		@Override
		public int compareTo(Point arg0) {
			return (int) (this.dist - arg0.dist);
		}

	}

	private double dist(Point a, Point b) {
		return Math.sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
	}

	@Override
	public void run() {
		try {
			in = new BufferedReader(new FileReader("spantree.in"));
			out = new BufferedWriter(new FileWriter("spantree.out"));

			int N = nextInt();
			Point[] point = new Point[N];
			double[] dist = new double[N];
			Arrays.fill(dist, Double.MAX_VALUE);
			boolean used[] = new boolean[N];

			for (int i = 0; i < N; i++) {
				point[i] = new Point(nextInt(), nextInt(), i);
			}

			dist[0] = 0;

			double sum = 0;

			for (int i = 0; i < N; i++) {
				int min = 0;

				for (int j = 0; j < N; j++) {
					if (!used[j] && (used[min] || (dist[j] < dist[min]))) {
						min = j;
					}
				}

				used[min] = true;
				sum += dist[min];

				for(int j=0; j<N; j++){
					if(!used[j] && dist(point[min],point[j]) < dist[j]){
						dist[j] = dist(point[min],point[j]);
					}
				}

			}

			out.write(sum + "\n");

			in.close();
			out.close();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public static void main(String[] args) {
		new Thread(new Spantree()).start();
	}

}