public static void Main()
Console.Write("Hay dem so luong chu so le cua so nguyen duong n.\nNhap n = ");
n = Convert.ToInt32(Console.ReadLine());
Console.Write("Khong hop le. Vui long nhap lai.\nNhap n = ");
n = Convert.ToInt32(Console.ReadLine());
if (n < 10) { Console.WriteLine("Ket qua la" + n); }
Console.WriteLine("Ket qua la: " + dem);