static void Main(string[] args)
{
SachGiaoKhoa sc = new SachGiaoKhoa();
sc.nhap();
sc.In();
Console.ReadLine();
}
static void Main(string[] args)
{
SachGiaoKhoa xd = new SachGiaoKhoa();
xd.nhap();
xd.In();
xd.tinhtien();
Console.ReadLine();
}
