How to select top 20 rows from a dataset in asp.net C#

How to select top 20 rows from a dataset in asp.net C#

DataSet ds = gn.fillGrid_with_param_DAL("Allotment_Distribution_view",
paramchk);
grd_Search.DataSource = ds.Tables[0].Select("Top 20");
grd_Search.DataBind();
I want to get top 20 rows from the dataset. In my dataset I am getting
records from database. I just need to select top 20 rows. Above is my code
that I am trying to bind top 20 rows to my grid but I am getting error as
missing operand after 20