Error Server tags cannot contain <% ... %> constructs. when accessing method from codebehind

I have a page  with
<asp:Label ID="Literal1" runat="server" Text="<%= ChangeAlphabet("") %>" />
and on codebehind i have method

 public string ChangeAlphabet(object str)     {         return "Hi";     }

I am not doing this with databinding.
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