var first = "абвшдеёжзийклмнопрстуфхцюьъэюя";
            var second = "";
            for (int i = 0; i < first.Length; i++)
            {
                if (i != first.Length)
                {
                    second = second + first[i + 1];
                }
                else
                {
                    second = second + first[0];
                }
            }
            first = second;