Given a string in roman no format (s)  your task is to convert it to an integer . Various symbols and their values are given below.
I 1
V 5
X 10
L 50
C 100
D 500
M 1000

Example 1:

Input:
s = V
Output: 5

Example 2:

Input:
s = III 
Output: 3

Your Task:
Complete the function romanToDecimal() which takes a string as input parameter and returns the equivalent decimal number. 

Expected Time Complexity: O(|S|), |S| = length of string S.
Expected Auxiliary Space: O(1)

Constraints:
1<=roman no range<=3999