Find number of symbols on Stage

Hi,

I'm trying to find out how many symbols with a certain naming convention are on the stage. The name of these symbols are incremented by 1, so for example I have symbols 'drag_1' & 'drag_2' currently on the stage and I want to return how many 'drag_ ' symbols are on the stage. This can change depending on how much of these symbols the user adds to the stage.

I've included some pseudo code below to help understand what im talking about!

for (var i = 0; i < 100; i++){

     if(SYMBOL_ON_STAGE = 'drag_' + i){

          number_of_symbols =  number_of_symbols + 1

     }

}

Thanks for any help!