Multiple If Statement Subject To Max Val

I've been asked to write a multiple if statement for someone here at work but I've been trying all day with no success. Basically, the OS liabilty in column C cannot exceed £2500. Here is an example inc the expected results............

So in row 1 the expected result is 500, as even though there is a 1000 reserve, 2000 of it has already been paid In row 2 nothing has been paid in column A so the OS liabilty in column C is the reserve up to a max of 2500 In row 3, there is 5000 in reserve, but 100 has been paid so the OS liability in col C must be 2000
In row 4 nothing has been paid in column A so the OS liability is the reserve in column B In row 5 150 has been paid, 150 is in reserve, so 150 is the OS liability
In row 6, 2500 has been paid, but even though there is an amount of 300 in reserve (col B), nothing is expected in OS liability as the 2500 max liability amount has been reached.