"use strict";
const Main = (input) => {
	let xs = input.trim().split(' ').map(v=>parseInt(v,10));
    let ans = '';
    if(xs[0] + xs[1] < 10){
    	ans = xs[0] + xs[1];
    }else if(xs[0] + xs[1] >= 10){
        ans = "error";
    }
    console.log(ans);
}
Main(require('fs').readFileSync('/dev/stdin','utf8'));