```
class Solution(object):
def romanToInt(self, s):
"""
:type s: str
:rtype: int
"""
# Conversion dictionary
r_to_i = {'I': 1,
'V': 5,
'X': 10,
'L': 50,
'C': 100,
'D': 500,
'M': 1000}
# Traverse the Roman numerals from right to left,
# Check if current numeral is smaller than previous.
# If smaller, subtract current from the sum.
# If greater, add current to the sum
s = s[::-1]
previous, current = r_to_i[s[0]], 0
sum = previous
for c in s[1:]:
current = r_to_i[c]
if current < previous:
sum -= current
else:
sum += current
previous = current
return sum
```