Forcing a chart to use the numbers I want

Hi,

So basically what I have is a chart like the one you can see in the attached image.
Now I don't want the chart to show all these numbers (10, 15, 20 etc.), but only show the numbers I wrote down (to the left): 1, 5, 12, 24, 35 and 40.

How do I do that?

Thanks,
David