DECLARE FUNCTION DES$ (ln$)
COLOR 15, 1: CLS
INPUT "Filename"; f$
OPEN f$ FOR INPUT AS #1
DO
LINE INPUT #1, d$
d$ = DES$(d$): PRINT d$
a = a + 1
IF a = 23 THEN SLEEP: a = 0
LOOP UNTIL EOF(1)
END

FUNCTION DES$ (ln$)
q = ASC(RIGHT$(ln$, 1))
ln$ = LEFT$(ln$, LEN(ln$) - 1)
FOR m = 1 TO LEN(ln$)
tt$ = tt$ + CHR$(ASC(MID$(ln$, m, 1)) - q)
NEXT m
DES$ = tt$
END FUNCTION