asp.net gridview column eval add 0s in front

trying to display '00001' in the gridview column from the database  where the value is only 1, 2, 3...etc
<asp:TemplateField HeaderText="Invoice No." SortExpression="invoiceno" ItemStyle-Width="180px" ItemStyle-HorizontalAlign="Center"> <ItemTemplate> <b><%# Eval("invoiceno")%></b> </ItemTemplate> </asp:TemplateField>