import java.io.*;
import java.util.StringTokenizer;

public class AlgoMSTB {
	public static void main(String[] args) throws IOException{new AlgoMSTB().run();
	}
		PrintWriter pw;
		StringTokenizer st;
		BufferedReader br;
		public void run() throws IOException {
			br=new BufferedReader(new FileReader("spantree.in"));
			pw = new PrintWriter(new File("spantree.out"));
			st=new StringTokenizer(br.readLine());
			int N=Integer.parseInt(st.nextToken());
			Element[] Adj=new Element[N+1];
			for (int i=1; i<N+1; i++){
				st = new StringTokenizer(br.readLine());
				int x1=Integer.parseInt(st.nextToken());
				int y1=Integer.parseInt(st.nextToken());
				Adj[i]=new Element(x1, y1);

			}
			Prim(Adj, N, 1);
			pw.println(sum);
			br.close();
			pw.close();
		}
		class Element{
			int x, y;
			Element(int x, int y){
				this.x=x;
				this.y=y;
			}
		}

		enum Color{WHITE,GRAY,BLACK};
		Color[] colors=new Color[5002];

        double d[]=new double[5002];
        int u;
        double sum=0;
        int p[]=new int[5002];
		void Prim(Element[] Adj, int N, int s){
			for (int i=1; i<N+1; i++) {
				if (i!=s) {
					d[i]=Double.MAX_VALUE;
				}else d[i]=0;
				colors[i]=Color.WHITE;
				p[i]=-1;
			}
			for (int i=1; i<N+1; i++){
			    double min=Double.MAX_VALUE;
			    for (int k=1; k<N+1; k++)
				    if ((d[k]<min)&&(colors[k]!=Color.BLACK)){
					  u=k;
					  min=d[k];
				  }
				colors[u]=Color.BLACK;
				for (int j=1; j<N+1; j++){
				  if (j!=u){
					double destin=Math.hypot(Adj[u].x-Adj[j].x, Adj[u].y-Adj[j].y);
					if ((d[j]>destin)&&(colors[j]==Color.WHITE)) {
						d[j]=destin;
						p[j]=u;
					}
				  }
				}
				if ( p[u]!=-1) sum=sum+Math.hypot(Adj[u].x-Adj[p[u]].x, Adj[u].y-Adj[p[u]].y);
			  }

		}


}