Arriving at the unit building where Li Qiyi lives, you find that the door downstairs is still closed. Without a magnetic card or knowing the password, you can only stand below and wait, hoping to see if other residents might pass by.
Not even a minute later, your phone rings: "Good son, are you downstairs at your sister's unit building?"
"Yeah, Mom, your timing is too precise!" You marvel at your mother's knack for mental arithmetic.
"Hmmph, your mother is a Math Olympiad mentor!" she says with great pride, "The passcode for the door is 174589."
"Got it."
After learning the passcode, you enter it on the keypad next to the card reader, and indeed, you hear a "beep," followed by a mechanical female voice saying: "Please enter."
Just as you open the door and hesitate about whether to close it, a crowd of people suddenly appears outside, both men and women. Realizing something's not right, you quickly shut the door.
"Hey, kid, open the door!"
