from itertools import *
keystream = [243, 186, 253, 51, 29, 40, 68, 168, 37, 32, 222, 183, 222, 12, 111, 185]
cipher = open('flag.pdf.enc','rb').read()
plain = open('flag.pdf','wb')

for i,j in zip( cipher , cycle(keystream) ):
    plain.write( chr( int(i.encode('hex'),16) ^ j ) )
#FLAG{15AD69452103C5DF1CF61E9D98893492}