```
import hashlib

version = "00000020"
previous_hash = "94c76b9fd810946630fe5d38748daf2541b36f20ab042a000000000000000000"
merkle_root = "d4d006dec8c23bcf1eef58de62939c8e436218527b7d04eacf12e5a88eaec0ed"
time = "1a45d15a"
bits = 'b72a5017'
nonce = "664c8064"

header_hex = version+previous_hash+merkle_root+time+bits+nonce
header_bin = header_hex.decode('hex')
hash = hashlib.sha256(hashlib.sha256(header_bin).digest()).digest()
print hash[::-1].encode('hex_codec') #0000000000000000000854f801e84750ffa9aaa97e74c36e975df3fa2ad5627c
print "flag: HZVI{"+header_hex+"}"
```