#include <complex>
#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
using namespace std;
typedef complex<double> Complex;
class compare_arg
{
  complex<double> current, prev;
public :
    compare_arg(Complex current, Complex prev){ this->current=current; this->prev=prev; }
  bool operator()(Complex c1, Complex c2)
  {
    if(current == prev)
      return arg(c1-current) < arg(c2-current);
    else return  arg((c1-current)/(current-prev)) < arg((c2-current)/(current-prev));
  }
};
main()
{
  int size;
  while(1)
    {
      int d = 0;
      cin >> size;
      if(size == 0) break;
      vector<Complex> v;
      for(int i=0;i<size;i++)
	{
	  double x, y;
	  cin >> x >> y;
	  v.push_back(Complex(x, y));
	}
      Complex current(0, 0);
      Complex prev(0, 0);
      for(int i=0;i<size;i++)
	{
	  sort(v.begin(), v.end(), compare_arg(current, prev));
	  Complex c = v.back(); v.pop_back();
	  double temp = abs(c-current);
	  d += (int)(temp*10) + (int)(temp*20) - (int)(temp*10)*2;
	  prev = current;	  
	  current = c;
	}
      cout << d/10 << "." << d%10 << endl;
    }
}