first:
INBOX
COPYTO   [23]
JUMPZ    second
BUMPUP   23
JUMP     first

second:
COPYTO   22

input:
INBOX
JUMPZ    end
COPYTO   20
SUB      [22]
JUMPZ    out2
JUMPN    output2

output1:
COPYFROM [22]
JUMPZ    end
OUTBOX
BUMPUP   22
JUMP     output1

output2:
COPYFROM 20

o2:
OUTBOX
INBOX
JUMPZ    end
JUMP     o2

out2:
COPYFROM 20
OUTBOX
BUMPUP   22
SUB      23
JUMPN    input

end: