double e = 2.718281828;
            double eps;
            double deltha = 0.5;
            double goldenRatio = (1 + Math.Sqrt(5)) / 2;
            double x0, a, b, q, l, r1, r2;
            bool condition = false;
            double f(double x)
            {
                return (Math.Pow(x, 5) + x - 3);
            }
            double derf(double x)
            {
                return (5*Math.Pow(x, 4) + 1);
            }

            Console.WriteLine("*SIMPLE ITERATION METHOD*");
            Console.WriteLine("Input precision");
            Console.Write("eps = ");
            eps = double.Parse(Console.ReadLine());
            Console.WriteLine("Input start of interval");
            Console.Write("a = ");
            a = double.Parse(Console.ReadLine());
            Console.WriteLine("Input end of interval");
            Console.Write("b = ");
            b = double.Parse(Console.ReadLine());
            x0 = (a + b) / 2;
            double a1 = a, b1 = b;

            while (Math.Abs(b1 - a1) > eps)
            {
                r1 = b1 - (b1 - a1) / goldenRatio;
                r2 = a1 + (b1 - a1) / goldenRatio;
                if (Math.Abs(derf(r1)) <= Math.Abs(derf(r2)))
                    a1 = r1;
                else
                    b1 = r2;
            }
            l = 1/ Math.Abs(derf((a1 + b1) / 2));

            double phi(double x)
            {
               return( x - l * (Math.Pow(x, 5) + x - 3));
            }
            double derphi(double x)
            {
                return (1 - l* (5 * Math.Pow(x, 4) + 1));
            }

            a1 = a;
            b1 = b;
            while (Math.Abs(b1 - a1) > eps)
            {
                r1 = b1 - (b1 - a1) / goldenRatio;
                r2 = a1 + (b1 - a1) / goldenRatio;
                if (Math.Abs(derphi(r1)) <= Math.Abs(derphi(r2)))
                    a1 = r1;
                else
                    b1 = r2;
            }
            q = Math.Abs(derphi((a1 + b1) / 2));


            if ((phi(x0) - x0) < deltha * (1 - q)) condition = true;
            else
            {
                condition = false;
                Console.WriteLine("Convergence condition is not implemented");
            }

            double x1 = 0;
            int i = 0;
            double abs = Math.Abs(x1 - x0);

            if (condition)
            {
              while(abs>=eps)
                {
                    i++;
                    x1 = phi(x0);
                    abs = Math.Abs(x1 - x0);
                    x0 = x1;
                    Console.WriteLine("x" + i + " = " +     Math.Round(x1, 8));


                }

                Console.WriteLine
                    (
                    "Approximated root: {0}; " +
                    "Number of iterations: {1}; " +
                    "Estimated number of iterations: {2};", Math.Round(x1, 8), i, Math.Round(Math.Log((b - a) / ((1 - q) * eps)) / Math.Log(1 / q), 0) + 1
                    );
            }
            Console.WriteLine();