Nope, you should send HTTP header 'SPbCTF' with value "Pretty cool"

Current HTTP headers: Array
(
    [Host] => kslweb1.spb.ctf.su
    [Connection] => close
    [Accept] => */*
    [User-Agent] => Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)
    [Accept-Encoding] => gzip, br, zstd, deflate
    [Referer] => http://kslweb1.spb.ctf.su/first/level6
    [Via] => 1.1 squid-proxy-5b96dc6d46-984kj (squid/6.13)
    [X-Forwarded-For] => 10.3.203.2
    [Cache-Control] => max-age=259200
)