Add a symbol to the highest y axis label value

Question

I have a bar chart with y axis labels like 10% 20% 30%.

But my requirement is to add the % symbol only to the top value of the y axis label. i.e 30%

Since it is a auto scaled chart. Iam not able to find a solution to implement this logic.

I am working on .Net webforms chartfx. Code in c#.

Any help is appreciated.