static class RandomExtension
    {
        public static double NextDouble(this Random r, int min, int max)
        {
            //return min + r.NextDouble() * (max - min);
            return r.Next(min + 1, max) - r.NextDouble();
        }

        public static double NextDouble(this Random r, double max)
        {
            return r.NextDouble() * max;
        }
    }