static void Main(string[] args)
 {
     do
     {
         int n;
         n = SoNguyen.NhapSoNguyenDuong("Nhap n=");
         if (TinhToan.ktdx(n))
         {
             Console.Write(n + " la so doi xung");
         }
         else
         {
             Console.Write(n + " khong la so doi xung");
         }
     } while (SoNguyen.NhapSoNguyen("\nTiep tuc (1.Tiep, 0.Khong)") != 0);
 }