static void Main(string[] args)
 {
     do
     {
         int a, b;
         a = SoNguyen.NhapSoNguyenDuong("Nhap a = ");
         b = SoNguyen.NhapSoNguyenDuong("Nhap b = ");
         Console.Write("UCLN(" + a + "," + b + ") = " + TinhToan.ucln(a, b));
     } while (SoNguyen.NhapSoNguyen("\nTiep tuc (1.Tiep, 0.Khong)") != 0);
 }