---

 int a = 5;
            int b = 12;
            int nod;

            while (a != b)
            {
                if (a > b)
                {
                    a = a - b;
                }
                else
                {
                    b = b - a;
                }
            }
            nod = a;

            Console.WriteLine($"НОД = {nod}");
            Console.ReadKey();