## Roman to Integer

Given a roman numeral, convert it to an integer.

Assume that **the input is always valid**.

## About Roman Numerals

Roman Numerals are represented by seven different symbols:

`I`

, `V`

, `X`

, `L`

, `C`

, `D`

, and `M`

.

For example, `2`

is written as II in Roman numeral.
`12`

is written as `XII`

, which is `X + II`

.

The number `27`

is written as `XXVII`

, which is `XX + V + II`

.

Roman numerals are usually written largest to smallest from left to right.
However, the numeral for four is not `IIII`

. Instead, the number four is
written as `IV`

because the one is before the five we subtract it making four.
The same principle applies to the number nine, which is written as `IX`

.

There are six instances where subtraction is used:

`I`

can be placed before `V`

(`5`

) or `X`

(`10`

) to make
`4`

or `9`

respectively.
`X`

can be placed before `L`

(`50`

) or `C`

(`100`

)
to make `40`

or `90`

respectively.
`C`

can be placed before `D`

(`500`

) or `M`

(`1000`

)
to make `400`

or `900`

respectively.

## Solution

## Helpers