INPUT s$
LET s$ = LTRIM$(RTRIM$(s$))
LET v = 0
FOR i = 1 TO LEN(s$)
   LET c$ = s$(i:i)
   LET k = POS("0123456789abcdef", c$)
   IF k > 0 THEN LET v = v*16 + k - 1
NEXT i
PRINT "S= ";s$, "V=";v

! Convert back to hex
LET hex$ ="0123456789abcdef"
LET hs$="                    "

FOR i = LEN(hs$) TO 1 STEP -1
   IF v = 0 THEN EXIT FOR
   LET d = MOD(v, 16) + 1
   LET hs$(i:i) = hex$(d:d)
   LET v = INT(v/16)
NEXT i
PRINT hs$
END