const romans = {
  I: 1,
  V: 5,
  X: 10,
  L: 50,
  C: 100,
  D: 500,
  M: 1000
}

const romanToInt = roman => {
  let result = 0, arr = roman.split('')
  for (let i=0; i<arr.length; i++) {
    result = romans[arr[i]] < (romans[arr[i + 1]] || 0)
      ? result - romans[arr[i]]
      : result + romans[arr[i]]
  }
  return result
}