How to handle duplicate TDictionary <string, Integer> error

Question

how to handle the error of duplicate value in the list. Values are fed into the input and entered into the list. If there is a duplicate then the value is renamed. eg:

procedure TForm2.Button1Click(Sender: TObject);
var
 CollectionNameTable : TDictionary<string, Integer>;
begin
  CollectionNameTable := TDictionary<string, Integer>.Create();
   try
     CollectionNameTable.Add('One', 1);
     CollectionNameTable.Add('TWO', 2);
     CollectionNameTable.Add('TWO', 3);
     CollectionNameTable.Add('FOUR', 4);
      except on E: EStringListError do
       begin
          ShowMessage( 'Дубликат!!!');
          CollectionNameTable.Add('DOUBLE_FREE', 3);
       end;

   end;

    CollectionNameTable.Clear;
    CollectionNameTable.Free;

end;