#[macro_use]
extern crate log;
extern crate env_logger;
extern crate rustc_serialize;

use rustc_serialize::hex::{FromHex, ToHex};
use std::io::{BufRead, stdin};

struct Pairwise<T: Iterator>(T);

impl<T> Iterator for Pairwise<T> where T: Iterator {
    type Item = (T::Item, T::Item);

    fn next(&mut self) -> Option<Self::Item> {
        if let (Some(fst), Some(snd)) = (self.0.next(), self.0.next()) {
            Some((fst, snd))
        } else {
            None
        }
    }
}

fn main() {
    env_logger::init().unwrap();
    let stdin = stdin();

    for (line1, line2) in Pairwise(stdin.lock().lines().filter_map(|x| x.ok())) {
        match (line1.from_hex(), line2.from_hex()) {
            (Ok(v1), Ok(v2)) => println!("{}", v1.iter().zip(v2).map(|(a, b)| a ^ b).collect::<Vec<u8>>().to_hex()),
            (Err(e), _) => error!("{}", e),
            (_, Err(e)) => error!("{}", e)
        }
    }
}