150-roman-and-arabic

Roman and Arabic

Challenge Description:

This challenge involves calculating the value of “aromatic” numbers which are a combination of Arabic digits and Roman numerals.
An aromatic number is of the form A₁R₁A₂R₂ ... A_nR_n, where each A_i is an Arabic digit, and each R_i is a Roman numeral. Each pair A_iR_i contributes a value described below, and by adding or subtracting these values together we get the value of the entire aromatic number.
An Arabic digit A can be 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9.
A Roman numeral R is one of the seven letters I, V, X, L, C, D, or M. Each Roman numeral has a base value: 1, 5, 10, 50, 100, 500, 1000, respectively.
The value of a pair AR is A times the base value of R. Normally, you add up the values of the pairs to get the overall value. However, wherever there are consecutive symbols ARA`R` with R` having a strictly bigger base value than R, the value of pair AR must be substracted from the total, instead of being added.
For example, the number 3M1D2C has the value 3 × 1000 + 1 × 500 + 2 × 100 = 3700 and 3X2I4X has the value 3 × 10 - 2 × 1 + 4 × 10 = 68 . Write a program that calculates the values of aromatic numbers.

Input sample:

The input is a valid aromatic number consisting of between 2 and 20 symbols. Your program should accept as its first argument a path to a filename. E.g.:

3M1D2C
2I3I2X9V1X

Output sample:

The output is the decimal value of the given aromatic number.

3700
-16