Shrink a PDF with gs

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dBATCH  -dQUIET -sOutputFile=output_document.pdf input_document.pdf 

I assume PDFSETTINGS can be adjusted but no clue how to find out what the options for that are.