use proconio::{input, marker::Chars};

fn main(){
    input!{
        s: Chars,
        t: Chars,
    }

    if s.len() == t.len(){
        let mut u = String::new();
        for i in 0..s.len(){
            u.push(s[i]);
            u.push(t[i]);
        }
        println!("{}", u);
    }else if s.len() == t.len()+1{
        let mut u = String::new();
        for i in 0..t.len(){
            u.push(s[i]);
            u.push(t[i]);
        }
        u.push(s[s.len()-1]);
        println!("{}", u);
    }else{
        println!("?");
    }
}