def decode(s):
    s = s[::-1]
    pre = 0
    cnt = 0
    for i in range(len(s)):
        n = D[s[i]]
        if n >= pre:
            cnt += n
        else:
            cnt -= n
        pre = n
    return cnt
    
def encode(m):
    lst = []
    for i in range(len(S)):
        n = m // num[i]
        if n <= 3:
            lst.extend([S[i]] * n)
        else:
            lst.append(S[i])
            lst.append(S[i - 1])
        m %= num[i]
        
    return "".join(lst)

N = int(input())
R = list(input().split())
num = [1, 5, 10, 50, 100, 500, 1000]
S = ["I", "V", "X", "L", "C", "D", "M"]
D = dict()
for i in range(len(S)):
    D[S[i]] = num[i]
    
R = list(map(decode, R))
M = sum(R)
if M >= 4000:
    print("ERROR")
    exit()
    
num.reverse()
S.reverse()
print(encode(M))