C# - Getting The Path Of A File Using Fileupload Control?

I am using a fileupload control to display the contents of a text file in a textbox..if i use this

<asp:FileUpload ID="txtBoxInput" runat="server" Text="Browse" />
string FilePath = txtBoxInput.PostedFile.FileName;

it will get only the file name like bala.txt.i need like this D:New Folderala.txt

Instead of fileupload control i have used textbox to get the path like this D:New Folderala.txt

<asp:TextBox ID="txtBoxInput" runat="server" Width="451px"></asp:TextBox>
string FilePath = txtBoxInput.Text;

But i need browse button instead of textbox to get the path..

EDIT:My button click event

protected void buttonDisplay_Click(object sender, EventArgs e)
{
string FilePath = txtBoxInput.PostedFile.FileName;
if (File.Exists(FilePath))
{
StreamReader testTxt = new StreamReader(FilePath);
string allRead = testTxt.ReadToEnd();
testTxt.Close();
}
}