F

// 4-2
            /*
            Console.WriteLine("Type your values:");
            Console.Write(" x = ");
            uint age = uint.Parse(Console.ReadLine());
            string[] ages = { " лет", " год", " года" };
            //int[] am = { 0, 1, 2, 2, 2, 0, 0, 0, 0, 0 };
            uint li = age % 10;
            uint ld = age / 10;
            uint idx;
            if ((li == 0) || (li >= 5 && li <= 9))
                idx = 0;
            else if (li == 1)
                idx = 1;
            else
                idx = 2;
            string[] dn = { "двадцать", "тридцать", "сорок", "пятдесят", "шесдесят" };
            string[] nn = { "", "один", "два", "три", "четрые", "пять", "шесть", "семь", "восемь", "девять" };
            Console.WriteLine("Results: " + dn[ld-2] + " " + nn[li] + " " + ages[idx]);
            */

            // 4-3
            /*
            Console.WriteLine("Type your values:");
            Console.Write(" (1 - R, 2 - D, 3 - L, 4 - S) e = ");
            uint e = uint.Parse(Console.ReadLine());
            Console.Write(" n = ");
            double n = double.Parse(Console.ReadLine());
            double r=0, d=0, l=0, s=0;
            switch (e)
            {
                case 1:
                    r = n;
                    d = 2 * r;
                    l = 2 * Math.PI * r;
                    s = Math.PI * Math.Pow(r, 2);
                    break;
                case 2:
                    d = n;
                    r = d / 2;
                    l = 2 * Math.PI * r;
                    s = Math.PI * Math.Pow(r, 2);
                    break;
                case 3:
                    l = n;
                    r = (l) / (Math.PI * 2);
                    d = 2 * r;
                    s = Math.PI * Math.Pow(r, 2);
                    break;
                case 4:
                    s = n;
                    r = Math.Sqrt(s / Math.PI);
                    d = 2 * r;
                    s = Math.PI * Math.Pow(r, 2);
                    break;
            }
            Console.WriteLine("Results: r = {0:0.##}, d = {1:0.##}, l = {2:0.##}, s = {3:0.##}",
                r, d, l, s);
            */