import java.io.*;
import java.util.*;
import java.text.*;

public class D_matsu{
	public static void main(String args[]) throws IOException{
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		solve(in);
	}
	
	private static void solve(BufferedReader in) throws IOException{
		int n;
		LinkedList l = new LinkedList();;
		double dist;
		
		DecimalFormat formatter = new DecimalFormat("#0.0");
		
		while(true){
			n = Integer.parseInt(in.readLine());
			if(n==0) break;
			
			for(int i=0;i<n;i++){
				int x,y;
				String line = in.readLine();
				StringTokenizer st = new StringTokenizer(line);
				x = Integer.parseInt(st.nextToken());
				y = Integer.parseInt(st.nextToken());
				Flag f = new Flag(x,y);
				l.addLast(f);
			}
			
			Flag prev = new Flag(0,-1);
			Flag now = new Flag(0,0);
			dist = 0;
			for(int i=0;i<n;i++){
				Flag next = nextFlag(prev,now,l);
				//System.out.println(next.x + "," + next.y);
				dist += now.distance(next);
				prev = now;
				now = next;
			}
			System.out.println(formatter.format(dist));
		}
		
		return;
	}
	
	private static Flag nextFlag(Flag prev, Flag now, LinkedList l){
		Flag next = (Flag)(l.getFirst());
		double argmin = Double.MAX_VALUE;
		ListIterator i = l.listIterator();
		ListIterator m;
		while(i.hasNext()){
			Flag f = (Flag)(i.next());
			double arg = Flag.arg(prev,now, f);
			//System.out.println(f.x+","+f.y+":"+arg);
			if(arg < argmin){
				next = f;
				argmin = arg;
			}
			else if(argmin==arg){
				if(now.distance(next) > now.distance(f)){
					next = f;
				}
			}
		}
		l.remove(next);
		return next;
	}
}

class Flag{
	int x;
	int y;
	
	Flag(int inx,int iny){
		x = inx;
		y = iny;
	}
	
	public static double arg(Flag f1, Flag f2, Flag f3){
		double arg1, arg2, ansarg;
		arg1 = Math.atan2(f2.y - f1.y, f2.x - f1.x);
		arg2 = Math.atan2(f3.y - f2.y, f3.x - f2.x);
		ansarg = arg1 - arg2;
		if(ansarg<0) ansarg += Math.PI*2;
		return ansarg;
	}
	
	public double distance(Flag f){
		return Math.sqrt((x - f.x)*(x - f.x) + (y - f.y)*(y - f.y));
	}
}