20 char mask-integer overflow

[nachorov027]

I have an exercice where with a given RSA1 hash i have to use brute force to crack it, we know the password is 18 random lower characters (but using space) and the last 2 characters are numbers

But y use this command and it doesnt work 
hashcat64.exe -m 100 -a 3 -d 1,2,3,4,5,6 -1 ?l?s hash ?1?1?1?1?1?1?1?1?1?1?1?1?1?1?1?1?1?1?d?d

And it said
integer overflow detected in keyspace of mask