How to implement switching radio stream 1 back 3 forward in an asterisk?

Question

Asterisk

Hello, I have the following code:

exten => 0,1,Macro(blkvm-clr,)
exten => 0,n,Set(__NODEST=)
exten => 0,n(ivrsel-0),Goto(ext-queues,708,1)

exten => 1,1,Macro(blkvm-clr,)
exten => 1,n,Set(__NODEST=)
exten => 1,n(ivrsel-1),Goto(ext-queues,700,1)

exten => 2,1,Macro(blkvm-clr,)
exten => 2,n,Set(__NODEST=)
exten => 2,n(ivrsel-2),Goto(ext-queues,701,1)

exten => 3,1,Macro(blkvm-clr,)
exten => 3,n,Set(__NODEST=)
exten => 3,n(ivrsel-3),Goto(ext-queues,702,1)

listening to different streams of radio stations is inconvenient to press from 1 to 9, Is it possible to somehow switch to 1 is back, 3 is forward?

Answer 1

arithmetic operations are available in the dialplan:
Accordingly, pull the current value and increment / decrement it depending on 1/3