How to show first parameter value in drop down list as a default value dynamically in ssrs report?

Hi,

in my ssrs report i have two parameters, accounts and Manager ,there is a cascading between the accounts parameter and manager parameter, as per the cascading we will get managers names based on the account we selected in the accounts parameter,

my requirement is the first name in the mangers drop down list  has to get selected as default value.

please help me with this, it is an urgent requirement.

Thanks in advance,

Naveen