class Solution(object):
    def romanToInt(self, s):
        num = 0
        i = len(s) - 1
        while(i >= 0):
            if s[i] == "I":
                num += 1
                i -= 1
            if s[i] == "V":
                if s[i - 1] == "I":
                    num += 4
                    i -= 2
                else:
                    num += 5
                    i -= 1
            if s[i] == "X":
                if s[i - 1] == "I":
                    num += 9
                    i -= 2
                else:
                    num += 10
                    i -= 1
            if s[i] =="L":
                if s[i - 1] == "X":
                    num += 40
                    i -= 2
                else:
                    num+= 50
                    i -= 1
            if s[i] == "C":
                if s[i - 1] == "X":
                    num += 90
                    i -= 2
                else:
                    num += 100
                    i -= 1
            if s[i] == "D":
                if s[i - 1] == "C":
                    num += 400
                    i -= 2
                else:
                    num += 500
                    i -= 1
            if s[i] == "M":
                if s[i - 1] == "C":
                    num += 900
                    i -= 2
                else:
                    num += 1000
                    i -= 1
        return num

        """
        :type s: str
        :rtype: int
        """