In the specification of DES, the key is represented as 64 bits, of which some are parity bits. Label all the bits (including parity bits) as k1, k2, ..., k64. If you knew the values of k1 through k16, but had to perform a brute force search through the other bits of the key, how long, in the worst case, would it take you to find the key, given that you can search through 220 keys in one second? Please express your answer in days, rounded to the nearest day.