Title of chart from Input Control table

I am using Vertical table as Input Control to chart. And wanted to display the name based on the selection of dimension from Input Control. Lets say, Input Control table has City and Sales and chart has sales breakdown by Month. When user clicks New york then the other one displays Monthly breakdown. Here I used the dimension name as Title in a cell for chart. This works fine in general. But I have Merged Dimension of City and when I use that it throws “not unique in the Report” and if I use the one of the dimension instead of Merged its throwing “Multivalve” Error.