Substr only returns up to 20

I have a thumbnail gallery and I’m trying to call thumbnails with ending numbers 0-300, however this strng will only call thumbnails up to twenty. Any idea what is wrong or how I could achieve this? Much appreciated!

this._name=“s”+(108);
a=int(this._name.substr(1,2)+(_root.album-1)*10);
pic.gotoAndStop(a);
stop();