Thea has a key on her calculator marked x. if an integer is displayed, pressing thex key chops off the first digit and moves it to the end. for example, if $6138$ is on the screen, then pressing the x key changes the display to $1386$. thea enters a positive integer into her calculator, then squares it, then presses the x key, then squares the result, then presses the key again. after all these steps, the calculator displays $243$. what number did thea originally enter?