Dynamic Drill Down On Crystal Report Using ASP.NET

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 ubove report at runtime(dynamic).
what i want If user will clicks on the 'London' value
I want to pass this value to my C# code so i can Run/Show another report based on this selection.
some one pls help me.
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