Work out the doomsday for 2023.

2023 → Tuesday.

Century anchor for the 2000s = Tuesday (2). YY = 23:

• q = 23 ÷ 12 = 1
• r = 23 − 12 = 11
• s = 11 ÷ 4 = 2
• Sum: 2 + 1 + 11 + 2 = 16, mod 7 = 2 = Tuesday.

Check: 2023's doomsday is Tuesday. ✓ (4/4/2023 was a Tuesday.)