What number cannot be written in Roman numerals?

DJH, There's also L = 50 C = 100 D = 500 Also a Line -- ABOVE a Letter MULTIPLIES that Number by 1,000 (ONE THOUSAND) Eg M with -- above it = 1,000 000 WHEREAS -- BELOW any Number DIVIDES that Number by 1,000 Eg M with -- Below it = 1 (ONE ) Divided by (ONE THOUSAND) m (ONE THOUSAND )

I enjoy writing the Roman numerals.

OK.. I thought it was 1 million