Only get the size from "du" command, not the folder names

Specifying both -k and -m does not make sense: either you want 1-Mbyte or 1-Kbyte blocks. Also -h does not make sense in combination with -k and -m. Only the last one -m will be considered

You can use cut to remove anything after the space:

du -sm /Users/JS_Admin/Desktop | cut -f1

With -f you specify which field you need (in this case the first one).