How I can get full path of file before upload

I Have a problem with my project ,


I have to upload file excel into server ,

but before upload file ,i want to recheck and validate the file using
eppplus ,
And i think i need to get the file path to validate it using epp,
how can i solve this ?

What I have tried:

This is my code ,

In my aspx file

 <dd style="text-align:left"> 
                                    <asp:fileupload id="FileUpload1" runat="server" width="90%" onchange="callme()"></asp:fileupload>
                                     <asp:RegularExpressionValidator   
                                  id="FileUpLoadValidator" runat="server"   
                                  ErrorMessage="Upload Jpegs and Gifs only."   
                                  ValidationExpression="^(([a-zA-Z]:)|(\\{2}\w+)\$?)(\\(\w[\w].*))(.xls|.xlsx)$"   
                                  ControlToValidate="FileUpload1">  
                                  </asp:RegularExpressionValidator> 

<pre> <asp:Button ID="btncheck" OnClick="uploadfile"  runat="server" Text="Cancel" CssClass="btn btn-primary"/>

this in on aspx.cs

protected void uploadfile(object sender, EventArgs e)
      {
          if (FileUpload1.HasFile)
          {
              string path = Server.MapPath("~/");
              string a = FileUpload1.PostedFile.InputStream.ToString();
              string fileexcel = FileUpload1.PostedFile.FileName;
              txtSchedule.Text = FileUpload1.PostedFile.FileName;
              string Path = HttpContext.Current.Request.PhysicalApplicationPath + FileUpload1.FileName;
              label1.Text = fileexcel;
          }
      }

Tags: C#, WebForms, ASP.NET, Microsoft Excel, FileIO