ASP.NET file upload size restriction

Question

I want to restrict users from uploading file sizes of more than 4MB, is there any way to do this without modifying the configuration file? I tried the code below to validate the file and response redirect but was still not able to make it. As long as I upload a file that is larger than 4MB it crashes when I click submit.

if(FileUpload1.PostedFile.ContentLength > 1234)
{
    FileUpload1.Attributes.Clear();
    Response.Redirect("Main.aspx");
}