string a = "517378";int max = 0;while (a.ToString().Length > 1){max = Convert.ToInt32(a.Substring(0, 1));a = a.Substring(1, a.ToString().Length - 1);if (max > Convert.ToInt32(a.Substring(0, 1))){a = a.Remove(0, 1).Insert(0, max.ToString());}}MessageBox.Show("Second Max Num is : "+max.ToString());