Given a string **S** representing a roman numeral. Convert S into integer.

**Problem Note **

**S**is guaranteed to be within the range from**1**to**3999**.- Roman numerals are represented by seven different symbools :

```
SYMBOL VALUE
I 1
V 5
X 10
L 50
C 100
D 500
M 1000
```

- For example, two is written as
`II`

in Roman numeral, just two one's added together. Twelve is written as,`XII`

, which is simply`X`

+`II`

. The number twenty seven 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, so we subtract one from five to make it 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.

**Example 1 **

```
Input: "III"
Output: 3
```

**Example 2**

```
Input: "IV"
Output: 4
```

**Example 3**

```
Input: "IX"
Output: 9
```

**Example 4**

```
Input: "LVII"
Output: 57
Explanation: L = 50, V= 5, II = 2.
```