Basically i need to do the following. If i have a list of cells which look like below:

£5000 Y

£10,000 N

£3,000 Y

£2,500 N

Total
£8000

What i want to be able to do is when i change the cell next to the amount (which has the Y or N), i need the total cell at the bootom to add up the only ones which have a Y next to it. Then, later if i was to change it to a N, the total would then subtract that figure, giving the new total
PLEASE PLEASE HELP!!!!!