Photoshop Smoothing Shortcut

This may sound basic, but I've not found an answer as of now…

Does anyone know what is the shortcut for the smoothing value of the brushes tool? Or is there is a way to set the shortcut for it?

I know that when the brush tool is selected:

1. to set OPACITY - Type 10 and the opacity goes to 10%

2. to set FLOW - Hold the Shift key and type 10 and flow goes to 10%

3. to set SMOOTHING - ??????

The only work around I can think of is setting an action for each value and associate each action to a shortcut, but that seems an overkill and actions shortcuts are quite precious for the work flow I use.  Also setting a shortcut with CTRL+ALT+CMD+F6 is a bit of an over kill just to change the smoothing value.

Any feed back would be greatly appreciated. !