roman to integer

public class  {
    public int romanToInt(String s) {
    int res = 0;
	for (int i = s.length() - 1; i >= 0; i--) {
		char c = s.charAt(i);
		switch (c) {
        	case 'I':
        		res += (res >= 5 ? -1 : 1);
        		break;
        	case 'V':
        		res += 5;
        		break;
        	case 'X':
        		res += 10 * (res >= 50 ? -1 : 1);
        		break;
        	case 'L':
        		res += 50;
        		break;
        	case 'C':
        		res += 100 * (res >= 500 ? -1 : 1);
        		break;
        	case 'D':
        		res += 500;
        		break;
        	case 'M':
        		res += 1000;
        		break;
		}
	}
	return res;
    }
}