Traintrain Software

## Writing rules

### to write in roman numerals

M=1000
D=500
C=100
L=50
X=10
V=5
I=1

A letter on the left of a bigger one is subtracted.
A letter on the right of a bigger one is added.
Examples:
IX=9, XI=11,
IV=4, VI=6,
XL=40, LX=60,
...

Please note that you can't subtract more than one letter.
Example:
8 isn't written IIX, but VIII

You can't add more than three identical letters.
Examples:
40 isn't written XXXX, but XL
9 isn't written VIIII, but IX

You should write first the thousands, next the hundreds, ...
Examples:
99 isn't written IC, but XCIX (XC=90 and IX=9)

More examples:

1789 is written MDCCLXXXIX
3333 is written MMMCCCXXXIII
2949 is written MMCMXLIX
454 is written CDLIV

Note: For numbers greater than thousand, we draw a line above letters V, X, L, C, D and M, their value will be multiplied by 1000. For values greater than a million, we frame it or draw two lines above, their value will be multiplied by a million. This software doesn't use these additional rules, and so the maximum value which can be correctly written is MMMCMXCIX (3999).

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