Suppose that each futures contract has a market value of $$0$ and a notional value of $$1,000,000.$ There are three traders $(x,Y,$ and $Z).$ Over one day, the following trades occur:

$x$ long, $Y$ short, $12$ contracts

$x$ long, $Z$ short, $4$ contracts

Y long, $Z$ short, $24$ contracts

$Y$ long, $x$ short, $21$ contracts

If these are the only trades that occur, what is the open interest?

$42$ contracts

$0$ contracts

$33$ contracts

$61$ contracts

$37$ contracts