MMXIX to 2019

Additive Rule: When a smaller or equal value follows a larger value, add them together. For example, VI = 5 + 1 = 6.

Subtractive Rule: When a smaller value appears before a larger value, subtract the smaller from the larger. For example, IV = 5 - 1 = 4.

Repetition Rule: Symbols can be repeated up to three times in succession. For example, III = 3, but 4 is written as IV, not IIII.