Dynamic Drill Down

i am working on Crystal Report Using ASP.NET.

I have a crystal report that looks like the following:

ID Contract Value CityName

P78 56 789 London

P99 378 999 San Diego

i am showing data on above report(A) at runtime(dynamic).

If user will clicks on the 'London' value, I want to pass/retrieve this value to my C# code so i can Run/Show another report(B) based on this selection.

some one pls help me.