Question 9
Define a domino to be a $1 \times 2$ rectangular block. A $2023 \times 2023$ square grid is filled with non-overlapping dominoes, leaving a single $1 \times 1$ gap. John then repeatedly slides dominoes into the gap; each domino is moved at most once. What is the maximum number of times that John could have moved a domino? (Example: In the $3 \times 3$ grid shown below, John could move 2 dominoes: D, followed by A.)
| A | B | C |
|---|---|---|
| D | | |
| A | B | C |
|---|---|---|
| D | | |