You can use IntegerSum function.

Here's an example.

Code
IF
	TimerFinished(_TimerEvent)
AND
	DB_GaervPlayerSpiritBottomsUp(_NPC,_TimerEvent,_DisplayText,_Trigger)
AND
	DB_GaervSitCount(_Count)
AND
	IntegerSum(_Count,1,_Sum)
AND
	_Sum < 5
AND
	DB_NumberString(_Sum,_NumberAsString)
AND
	StringConcatenate(_DisplayText,_NumberAsString,_ResultingDisplayText)
THEN
	NOT DB_GaervSitCount(_Count);
	DB_GaervSitCount(_Sum);
	TimerCancel(_TimerEvent);
	CharacterDisplayText(_NPC,_ResultingDisplayText);
	TimerLaunch(_TimerEvent,6000);

https://kamesama.github.io/dos2-team-builder/