var num = thisComp.layer("dummy").text.sourceText;
 num = Comma(num);
 [num]
 
 function Comma(number)
    {
    number = '' + Math.round(number);
    if (number.length > 3)
       {
       var mod = number.length % 3;
       var output = (mod > 0 ? (number.substring(0,mod)) : '');
       for (i=0 ; i < Math.floor(number.length / 3); i++)
           {
           if ((mod == 0) && (i == 0))
                output += number.substring(mod+ 3 * i, mod + 3 * i + 3);
           else
                output+= ',' + number.substring(mod + 3 * i, mod + 3 * i + 3);
           }
       return (output);
       }
    else return number;
    }