#!/usr/bin/env lua

s = io.read("*line")
nlist = {}
j = 1
for i in string.gmatch(s, "%S+") do
    nlist[j] = tonumber(i)
    j = j + 1
end

if nlist[1] + nlist[2] >= 10 then
    print("error")
else
    print(nlist[1]+nlist[2])
end