Q-21.12.3. Today, an exchange introduced a new futures contract. The open interest started at zero. Because it is a new contract, there were only the following four trades:

• Trader Adam (TA) buys (aka, takes a long position in) 1,000 contracts from Trader Betty (TB), who is the seller (aka, takes a short position), and both are new positions
• Trader Charles (TC) buys 300 contracts, in a new position, from Trader Adam (TA), who closes out 300 of his contracts
• Trader Denise (TD) sells 225 contracts, in a new position, to Trader Betty (TB), the buyer who closes out 225 of her contracts
• Trader Betty (TB) delivers on 175 of her short contracts to Trader Adam (TA), who takes delivery on 175 of his long contracts

What is the open interest, after the above four trades, at the end of the day?