using System;
using System.Linq;

public class RomanNumeral
{
    const int NaN = -1;
    private static int ToInteger(string roman_numeral) {
        string ro_num = roman_numeral.ToUpper().Trim();
        char[]  ro_num_array = ro_num.ToCharArray();
        if (ro_num == "N") { return 0; }
        
        char[] symbols = { 'I', 'V', 'X', 'L', 'C', 'D', 'M' };
        int [] values = { 1, 5, 10, 50, 100, 500, 1000 };
        int int_num = 0;
        int symb_it = 0, symb_consec = 0;
    
        bool to_parse = true;
        int subtrahend = 0, didgit = -1;
        foreach (char ro_num_char in ro_num_array.Reverse<char>()) {
            Console.WriteLine(ro_num_char);
            do
            {
                if (ro_num_char == symbols[symb_it])
                {
                    symb_consec += (symb_it%2==1)? 3:1;
                    if (symb_consec > 3) {
                        Console.WriteLine("symb_consec>3");return NaN; 
                    }
                    didgit = symb_it/2*2+2;
                    Console.WriteLine("Didgit: " + didgit);
                    
                    subtrahend = ((symb_it-1)/2)*2;
                    int_num += values[symb_it];
                    to_parse = false;
                    Console.WriteLine(values[symb_it]);
                } 
                else if ((ro_num_char == symbols[subtrahend]))
                {
                    if (didgit == symb_it) { return NaN; }
                    didgit = symb_it;
                    
                    int_num -= values[subtrahend];
                    to_parse = false;
                    //Console.WriteLine(over_six);
                }
                if (to_parse) {
                    symb_it++;
                    if (symb_it > 6) { Console.WriteLine("symb_it>6");return NaN; }
                    symb_consec = 0;
                }
            } while (to_parse);
            
            to_parse = true;
        }
        return int_num;
    }
    public static void Main()
    {
        int test = RomanNumeral.ToInteger("MMCMXCIV");
        Console.WriteLine(String.Format("{0:D0}",test));
    }
}