def roman_to_int(s):
romans = {'I': 1,
'V': 5,'X': 10,
'L': 50, 'C': 100,
'D': 500, 'M': 1000}
result = 0
prev_value = 0
for c in s[::-1]:
value = romans[c]
if value < prev_value:
result -= value
else:
result += value
prev_value = value
return result