static void Main(string[] args)
 {
     do
     {
         int n;
         n = SoNguyen.NhapSoNguyenDuong("Nhap n=");
         Console.Write("So luong chu so le cua " + n + " la " + TinhToan.dem(n));
     } while (SoNguyen.NhapSoNguyen("\nTiep tuc (1.Tiep, 0.Khong)") != 0);
 }