using System;

using System.Collections.Generic;

using System.Text;

public class Program

{

    public static void Main()

    {

        string str = "CD";

        var list = new Dictionary<char,int>(){

            {'I',1},{'V',5},{'X',10},{'L',50},{'C',100},{'D',500},{'M',1000}

        };

        int num = 0;

        if(str.Length > 1){

                for(int i=0; i<str.Length;i++){

                    var ch = str[i];

                    num = list[ch] + num;

​

                    if(i != 0)

                    {

                        var prevch = str[i-1];

                        if(list[ch] > list[prevch]){

                            num = num - (2*list[prevch]);

                        }

                    }

                }

            }

​

        Console.WriteLine(num);

    }

}

​