Roman to Integer

Roman numerals are represented by seven different symbols: `I`, `V`, `X`, `L`, `C`, `D` and `M`. | Symbol | Value | |--------|-------| | I | 1 | | V | 5 | | X | 10 | | L | 50 | | C | 100 | | D | 500 | | M | 1000 | For example, `2` is written as `II` in Roman numeral, just two ones added together. `12` is written as `XII`, which is simply `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) and `X` (10) to make 4 and 9. - `X` can be placed before `L` (50) and `C` (100) to make 40 and 90. - `C` can be placed before `D` (500) and `M` (1000) to make 400 and 900. Given a roman numeral, convert it to an integer.