static void Main(string[] args)
        {
            Console.WriteLine("I'm the first decimal number");
            const long a = 102.12345678901234567777777889;
            Console.WriteLine(a.ToString());

            Console.WriteLine("I'm the second decimal number");
            const long b = 112.1234784960123456777777889;
            Console.WriteLine(b.ToString());

            Console.WriteLine("I'm the first double number");
            double c = 102.123467890;
            Console.WriteLine(c.ToString());

            Console.WriteLine("I'm the second double number");
            double d = 2.601234678897777;
            Console.WriteLine(d.ToString());

            Console.WriteLine("I'm the Log result after Convert");
            (вот операция, о которой упоминалось выше)
            double lenth_1 = (Math.Floor(2 - Math.Log((double)(a - b)) / Math.Log(10, Math.E))); 
            Console.WriteLine(lenth_1.ToString());
            Console.Read();