10
20 REPEAT:INPUT":"A$:PRINTFNrot13(A$):UNTIL0
30 :
40 DEFFNrot13(A$)
50 LOCAL A%,B$,C$,D$
60 FOR A%=1 TO LEN A$
70 B$=MID$(A$,A%,1):C$=B$
80 IF (B$>="A" AND B$<="M")OR(B$>="a" AND B$<="m"):C$=CHR$(ASCB$+13)
90 IF (B$>="N" AND B$<="Z")OR(B$>="n" AND B$<="z"):C$=CHR$(ASCB$-13)
100 D$=D$+C$:NEXT:=D$