For each port number in stdin, print the well-known service name (or 'unknown').
Build a mini service lookup. Mapping (lowercase service names):
`21=ftp, 22=ssh, 23=telnet, 25=smtp, 53=dns, 80=http, 110=pop3, 143=imap, 443=https, 3306=mysql, 5432=postgres, 6379=redis, 8080=http-proxy`
Anything not in the table → `unknown`. Read one port per line, print one service per line in the same order.
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