How to convert result of addition to a zero if answer is a minus figure

Hi, I'll try to explain my problem. I'm putting together a calculator for work, which has a starting figure of £40,000, and then has three cells in which the number input is deducted from the £40,000.

The trouble is that if the three cell's total number exceeds the 40,000, it shows as a minus figure, whereas I want the field to just show a zero, as it is basically a 'amount on which tax is now due' query, over a period of three years, in which each of the years needs to be shown.

For context, the cells are as follows:

G59 = £40,000
G61 = cell figure to be deducted from £40,000
G63 = cell figure to be deducted from £40,000
G65 = cell figure to be deducted from £40,000
G67 = remaining amount for tax due.

So I've put in G59-G61-G63-G65 to find the amount due, but want the figure to autocorrect to £0.00 is the result is a minus figure.

Please someone help!!!

Thank you

Amazing!! Thank you so much!