#!/usr/bin/env python3
roman_table = [
    ('M', 1000),
    ('CM', 900),
    ('D', 500),
    ('CD', 400),
    ('C', 100),
    ('XC', 90),
    ('L', 50),
    ('XL', 40),
    ('X', 10),
    ('IX', 9),
    ('V', 5),
    ('IV', 4),
    ('I', 1),
]
def roman_to_int(s):
    n = 0
    for c, e in roman_table:
        while s.startswith(c):
            s = s[len(c) :]
            n += e
    assert not s
    return n
def int_to_roman(n):
    s = ''
    for c, e in roman_table:
        s += c * (n // e)
        n %= e
    assert not n
    return s

_ = int(input())
rs = input().split()
acc = sum(map(roman_to_int, rs))
if acc >= 4000:
    result = 'ERROR'
else:
    result = int_to_roman(acc)
print(result)