set specific value in value axies in chart

Hi

I want to reduce extra space in my chart with customizing minimum range for value axis and as we want to chart seems more natural ;instead of 0 for minmum number we interact it with constant number like 1

min range=min(value field) -(specific number )

the output of min function in jasper is NUMBER

my value field is double

I tried alot for cast and subtract but it doesn't work !

I would appreciate if anybody could help me

thanks in advance