10 S=0
20 INPUT N$:IF N$="" THEN 70
30 N$="&H"+N$:N=VAL(N$)
40 S=S+N
50 IF S>255 THEN S=S-256
60 GOTO 20
70 S=NOT S:S=S+1
80 S$=HEX$(S)
90 PRINT RIGHT$(S$,2)