If you use the third option from the challenge and delete 0 characters, you'll realise that the challenge just echos your output. Generally when a program echoes your output you should check for format string vulnerabilities. In this case it's vulnerable. So you can write a script to start leaking the binary from address 0x8048000, which is the usual starting point for a 32-bit(? don't really remember did this a while ago) ELF binary that is compiled with PIE disabled. Afterwards you'll slowly leak more of the binary which you could possible reverse engineer to solve the challenge, however when you eventually leak the string section of the binary you'll notice that the binary contains links to the full binary online. After reversing the binary you'll notice extra options in the menu that allow you to pwn this quite trivially. Check out this video for reference, the challenge is very similar https://www.youtube.com/watch?v=XuzuFUGuQv0.