Type in your shoe size (European, without decimals) on the calculator and double it. Press "=". In my case 45 * 2 = 90

Add 40. Press "=". In my case 90 + 40 = 130

Time it with 50. Press "=". In my case 130 * 50 = 6500.

Subtract your birth year. Press "=". In my case 6500 - 1997 = 4503

Add the number of years since the millennium (12). Press "=". In my case 4503 + 12 = 4515(!)