40 (a1) 15(b1) 25(c1)

I wanted it this way b1 = a1-c1 and c1 = a1-b1
so whenever I make a change in either b1 or c1, it automatically fixed the other cell and make the total of A1

But when I put the formulas, I get the 'Circular Reference Warning', I click okay but then the functions don't work properly. It only works for either b1 or c1. Is there anyway that I can make both work together.

Ex. 40 15 25 (if I make it 26 from 25, it'll change 15 into 14)
40 14 26 (and again if I make 14, 12, it'll automatically, change 26 into 28)
40 12 28

Thanks in advance!