Natas 23's welcome page is just a Password form with a login button:
Looking at the source code, it looks like the credentials to Natas 24 will be given if our "passwd" parameters passes two checks:
- PASSWD must contain the substring "iloveyou"
- PASSWD > 10 must evaluate to be true
Looking through some PHP documentation, it seemed like 1e10 is valid notation and will pass the second check.
I tried a few random things, but the one that worked was appending "iloveyou" to "1e10" like this: