using System;

namespace SerieDeux
{
	class MainClass
	{
		public static void Main (string[] args)
		{
			double precision = 1E-15;
			double somme = 0;
			double terme = 1;
			while (terme > precision)
			{
				somme += terme;
				terme /= 2;				
			}
			Console.WriteLine(somme);
		}
	}
}