can I make this so the vm would not be not responsibe when running the tests

Hello, For a exercism challenge I need to calculate the total grains on a chessboard. So I did : atSquare: anInteger     self validateInput: anInteger.     ^ anInteger = 1         ifTrue: [ 1 ]         ifFalse: [ 2 * (self atSquare: anInteger - 1) ] but when I run the tests , the vm seems to be not responsive for some 4 - 5 seconds. Is there a way I can use this code and take care that the vm stays responsive. Regards, Roelof