R2I_TBL = {
  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,
}
I2R_TBL = R2I_TBL.invert

def roman2i(roman)
  roman.scan(/IV|IX|XL|XC|CD|CM|I|V|X|L|C|D|M/).map{|s|
    R2I_TBL[s.intern]
  }.sum
end

def i2roman(n, s="")
  if n > 0
    i, c = I2R_TBL.find{|k,v|k <= n}
    i2roman(n - i, s + c.to_s)
  else
    s
  end
end

N = gets.to_i
R = gets.split.take(N)

total = R.map{|r|roman2i(r)}.sum
puts total > 3999 ? :ERROR : i2roman(total)