How do i limit # of MCs?

well i have this code


rand=Math.round(Math.random()*10);
if(rand==1){
duplicateMovieClip("glowdrop", "glowdrop" add x, x);
setProperty("glowdrop" add x, _x, random(550));
x = Number(x)+1;
}
if(rand==2){
duplicateMovieClip("glowdrop2", "glowdrop2" add x, x);
setProperty("glowdrop2" add x, _x, random(550));
x = Number(x)+1;
}

how do i limit the # of movie clips that can appear on the stage at one time?