How ancient Romans used to write numbers.
I means 1, V means 5, X means 10, L means 50, C means 100, D means 500 and M means 1000
Example: 2025 = MMXXV
When a smaller-valued symbol appears before a larger, it is subtracted
Example: XL = L − X = 50 − 10 = 40
We still use them today in special places, like numbering important events such as the Olympic Games, and sometimes on clocks and books.