leetcode-Roman to Integer

Given a roman numeral, convert it to an integer.
Input is guaranteed to be within the range from 1 to 3999.

class Solution {
    public int romanToInt(String s) {
        int sum = 0;
        if(s.indexOf("IV")!=-1) sum -=2;
        if(s.indexOf("IX")!=-1) sum -=2;
        if(s.indexOf("XL")!=-1) sum -=20;
        if(s.indexOf("XC")!=-1) sum -=20;
        if(s.indexOf("CD")!=-1) sum -=200;
        if(s.indexOf("CM")!=-1) sum -=200;
        for(int i=0; i<s.length(); i++){
            if(s.charAt(i)=='I') sum +=1;
            if(s.charAt(i)=='V') sum +=5;
            if(s.charAt(i)=='X') sum +=10;
            if(s.charAt(i)=='L') sum+=50;
            if(s.charAt(i)=='C') sum+=100;
            if(s.charAt(i)=='D') sum+=500;
            if(s.charAt(i)=='M') sum+=1000;
        }
        return sum;
    }
}