import java.io.*;
import java.util.*;
import java.text.*;
import static java.lang.Math.*;

public class D_matsu_2{
	public static void main(String args[]) throws IOException{
		Scanner sc = new Scanner(System.in);
		solve(sc);
	}
	
	private static void solve(Scanner sc) throws IOException{
		int n;
		LinkedList<Flag> l = new LinkedList<Flag>();
		double dist;
		
		DecimalFormat formatter = new DecimalFormat("#0.0");
		
		while(true){
			n = sc.nextInt();
			if(n==0) break;
			
			for(int i=0;i<n;i++){
				int x,y;
				x = sc.nextInt();
				y = sc.nextInt();
				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);
				dist += now.distance(next);
				prev = now;
				now = next;
			}
			System.out.println(formatter.format(dist));
		}
		
		return;
	}
	
	private static Flag nextFlag(Flag prev, Flag now, LinkedList<Flag> l){
		Flag next = l.getFirst();
		double argmin = Double.MAX_VALUE;
		for(Flag f : l){
			double arg = Flag.arg(prev,now, f);
			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;
	}
	
	//f2f3とf1f2のなす偏角
	public static double arg(Flag f1, Flag f2, Flag f3){
		double arg1, arg2, ansarg;
		arg1 = atan2(f2.y - f1.y, f2.x - f1.x);
		arg2 = atan2(f3.y - f2.y, f3.x - f2.x);
		ansarg = arg1 - arg2;
		if(ansarg<0) ansarg += PI*2;
		return ansarg;
	}
	
	//fとの距離
	public double distance(Flag f){
		return sqrt((x - f.x)*(x - f.x) + (y - f.y)*(y - f.y));
	}
}