import re
from typing import Set

def parse_logs(logs: str) -> Set[str]:
    current_users = set()
    join_pattern = r'(?<=:)([^:()]*)(?=\()(?=.*\bAuthenticated\b)'
    leave_pattern = r'(?<=:)([^:()]*)(?=\()(?=.*\bConnection closed\b)'

    for line in logs.splitlines():
        line = line.strip()

        join_match = re.search(join_pattern, line)
        if join_match:
            username = join_match.group(1)
            current_users.add(username)

        leave_match = re.search(leave_pattern, line)
        if leave_match:
            username = leave_match.group(1)
            current_users.discard(username)

    return current_users