using System;
using System.Linq;

namespace Yuki
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string a = Console.ReadLine().Trim(' ');

            a = a.Replace("CM", "DCCCC");
            a = a.Replace("CD", "CCCC");
            a = a.Replace("XC", "LXXXX");
            a = a.Replace("XL", "XXXX");
            a = a.Replace("IX", "VIIII");
            a = a.Replace("IV", "IIII");

            string ans = "";
            int cnt = a.Count(x => x == 'M');
            while (cnt > 0)
            {
                ans += "M";
                cnt--;
            }

            cnt = a.Count(x => x == 'D');
            while (cnt > 0)
            {
                ans += "D";
                cnt--;
            }

            cnt = a.Count(x => x == 'C');
            while (cnt > 0)
            {
                ans += "C";
                cnt--;
            }

            cnt = a.Count(x => x == 'L');
            while (cnt > 0)
            {
                ans += "L";
                cnt--;
            }

            cnt = a.Count(x => x == 'X');
            while (cnt > 0)
            {
                ans += "X";
                cnt--;
            }

            cnt = a.Count(x => x == 'V');
            while (cnt > 0)
            {
                ans += "V";
                cnt--;
            }

            cnt = a.Count(x => x == 'I');
            while (cnt > 0)
            {
                ans += "I";
                cnt--;
            }

            ans = ans.Replace("IIIII", "V");
            ans = ans.Replace("VV", "X");
            ans = ans.Replace("XXXXX", "L");
            ans = ans.Replace("LL", "C");
            ans = ans.Replace("CCCCC", "D");
            ans = ans.Replace("DD", "M");

            ans = ans.Replace("DCCCC", "CM");
            ans = ans.Replace("CCCC", "CD");
            ans = ans.Replace("LXXXX", "XC");
            ans = ans.Replace("XXXX", "XL");
            ans = ans.Replace("VIIII", "IX");
            ans = ans.Replace("IIII", "IV");

            if (ans.Contains("MMMM")) ans = "ERROR";

            Console.WriteLine(ans);
        }
    }
}