Minimum and Maximum Numbers of Roles
Some scripts require an exact number of male or female characters, however some characters can be played male or female.
Consequently, the result of your search will tell you the minimum number of male and female characters, and the total minimum characters (with and without doubling), leaving you to sort out which are played male and which female.
If you want an exact number of parts, then set the minimum and maximum to the same number.
(This is a constraint, so, like every other constraint, will reduce the number of scripts available to you!)