public static void Main()
Console.Write("Nhap mot nam bat ky de kiem tra: ");
chk_year = Convert.ToInt32(Console.ReadLine());
if ((chk_year % 400) == 0)
Console.WriteLine("{0} la nam nhuan.\n", chk_year);
else if ((chk_year % 4) == 0 && (chk_year % 100) != 0)
Console.WriteLine("{0} la nam nhuan.\n", chk_year);
Console.WriteLine("{0} khong phai la nam nhuan.\n", chk_year);