#!/usr/bin/python3

import sys
import re

if __name__ == '__main__':
    if len(sys.argv)>1:
        flag = sys.argv[1]
        if flag and flag[0] == '!':
            flag = flag[1:]
        if flag not in ['syn', 'ack', 'rst', 'fin', 'urg', 'psh', 'ecn', 'cwr']:
            print(f'Error: {flag} is not a valid TCP flag')
            sys.exit(1)
    else:
        sys.exit(2)

    sys.exit(0)