hum... you are right, indeed.Out of interest, is the amount you win related in any way to the amount you bet? The OP seems to be saying that the closest bet wins all of everyone else's money. If this is the case, what is the downside to betting the minimum amount every time?
amount you bet: A
quantity of dollahz in teh box: b
if you win, you will get the following: b+Ax2.
let's say: if you win, and there are 100 dollahz in teh box, and you contributed with 40 dollahz, instead of 100 dollahz you will get 180 dollahz, 80 being the quantity you bet x2.
in teh box we currently have vincent's 10 dollahz and gianlucad's 100 dollahz( I have forgiven his 400 dollahz debt, how could he ever pay for it?), thus making 110 dollahz. also, we have 2 kidneys.