// Roman to Integer — EASY
// Category: math
Roman numerals are represented by seven symbols: `I=1, V=5, X=10, L=50, C=100, D=500, M=1000`.
Given a roman numeral string, convert it to an integer.
Subtraction rules: `IV=4`, `IX=9`, `XL=40`, `XC=90`, `CD=400`, `CM=900`.
Example: s = "III"
Output: 3