Macro for flash PSTN

Hi everyone,

I am able to use feature.conf like below to flash PSTN incoming and outgoing calls separately.
inflash => *4,caller,Flash,()
outflash => *3,callee,Flash,()[/ul]

Instead of using *3 and *4, I want use single keymap to flash PSTN calls. I want to write a macro as following
[ul]zapflash => ##,self,Macro,myflash[/ul]

In [macro-myflash] I want of find out if caller or callee is the zap channel and flash it. I have no clue on how to write this macro. Please help.