Convert numbers to Roman numerals and Roman numerals back to numbers.
Seven letters represent fixed values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Numerals are normally written largest to smallest, added together (VI = 5+1 = 6). When a smaller value appears immediately before a larger one, it's subtracted instead (IV = 5−1 = 4), which keeps no symbol repeated more than three times in a row.
Standard Roman numerals repeat symbols to build up values, and M (1,000) is the largest single letter — so 3,999 (MMMCMXCIX) is the largest number expressible without inventing extra notation. Numbers above that historically used a bar (vinculum) over a numeral to multiply it by 1,000, which isn't supported here.
Not in the standard system used here (which uses "IV") — though "IIII" does appear traditionally on some clock faces for visual symmetry.
No — the classical system has no symbol for zero and no notation for negative values.
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