HP 50G help

[Hlib]

From HP50g / 49g+ / 48gII graphing calculator
advanced user’s reference manual, chapter "RPL Programming 1-44,45":

Example: The following program executes INPUT to prompt for a social security number, then extracts two
strings: the first three digits and last four digits.

<<
"Key in S.S. #"
{ " - - " -1 }

INPUT
DUP 1 3 SUB
SWAP
8 11 SUB

>>

Calculator returns
[ INPUT Error:
Bad Argument
Type ]

I tried to edit many times, only to plunge more deeply into the mire of HP's manuals. So, can any one to help me in this case?