#!/usr/bin/env python3


MAX_NUM = 3999
ROMAN_VALS = (('I', 1), ('IV', 4), ('V', 5), ('IX', 9), ('X', 10), ('XL', 40),
              ('L', 50), ('XC', 90), ('C', 100), ('CD', 400), ('D', 500),
              ('CM', 900), ('M', 1000))[::-1]


def roman2arabic(roman):
    res = 0
    for s, v in ROMAN_VALS:
        while roman.startswith(s):
            res += v
            roman = roman[len(s):]
    return res


def arabic2roman(x):
    res = ""
    for s, v in ROMAN_VALS:
        d, x = divmod(x, v)
        res += d * s
    return res


def sum_romans(romans):
    s = sum(roman2arabic(roman) for roman in romans)
    if s > MAX_NUM:
        return None
    else:
        return arabic2roman(s)


def main():
    _ = input()
    res = sum_romans(input().split())
    print("ERROR" if res is None else res)


if __name__ == '__main__':
    main()