Webi Input Control Issue

Hello Everyone,

I have a Tree Map  chart which has the value of Sales and Material Sub Category. Now I have an Input Control of Country for this Chart as follows :

Now, for the title of the chart i have written a formula so that if the country from the left changes,title will change accordingly for the chart.If i select any one country the title will change as shown above, if i select (Select All) the title will show  "For All Countries" as below:

Now my problem is if select more than one country at a time ,the title is showing me #MULTIVALUE error. So, what should be done or any formula suggested to be written in the title so that it gives me both the values in the title if i select two countries at a time.

I tried out many things but nothing helped.A suggestion or a reply would be a great help.Since its very urgent.

Thanks & Regards,

Foram Shah