def read_roman(s):
    table = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000, 'IV': 4, 'IX': 9, 'XL': 40, 'XC': 90, 'CD': 400, 'CM': 900}
    num = 0
    while s:
        for c in sorted(table)[::-1]:
            if s.startswith(c):
                num += table[c]
                s = s[len(c):]
                break
    return num

def print_roman(num):
    table = {1: 'I', 5: 'V', 10: 'X', 50: 'L', 100: 'C', 500: 'D', 1000: 'M', 4: 'IV', 9: 'IX', 40: 'XL', 90: 'XC', 400: 'CD', 900: 'CM'}
    s = ""
    while num:
        for n in sorted(table)[::-1]:
            if num >= n:
                num -= n
                s += table[n]
                break
    print(s)

n = int(input())
ans = 0
for r in input().split(' '):
    ans += read_roman(r)
if ans < 4000:
    print_roman(ans)
else:
    print("ERROR")