After reading the scrypt documentation carefully, I found that I completely misunderstood how it works.
> In this case, the last operator of scriptSig has to be the index of the public function called, starting from 1. For example, if public function larger is called, scriptSig of y 3 can fulfill the contract below, in which 3 is the public function index.
<a href='https://scryptdoc.readthedocs.io/en/latest/intro.html#multiple-public-functions'>https://scryptdoc.readthedocs.io/en/latest/intro.html#multiple-public-functions</a>.
After reading the scrypt documentation carefully, I found that I completely misunderstood how it works.
> In this case, the last operator of scriptSig has to be the index of the public function called, starting from 1. For example, if public function larger is called, scriptSig of y 3 can fulfill the contract below, in which 3 is the public function index.
<a href='https://scryptdoc.readthedocs.io/en/latest/intro.html#multiple-public-functions'>https://scryptdoc.readthedocs.io/en/latest/intro.html#multiple-public-functions</a>.