a=[1000,900,500,400,100,90,50,40,10,9,5,4,1]
r=%w(M CM D CD C XC L XL X IX V IV I)
b=[]
gets
gets.split.map{|n|
x=0
j=0
loop{
if n.start_with?(r[j])
x+=a[j]
n=n[r[j].size..n.size-1]
break if n==""
else
j+=1
end
}
b<<x
}

e=c=b.inject(:+)
d=""
i=0
loop{
if c<1
break
elsif a[i]<=c
d+=r[i]
c-=a[i]
else
i+=1
end
}
puts e>3999?"ERROR":d