#!/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)