import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        char[] a = sc.next().toCharArray();
        char[] b = sc.next().toCharArray();
        if (a.length < b.length || a.length > b.length + 1) {
            System.out.println("?");
            return;
        }
        char[] ans = new char[a.length + b.length];
        for (int i = 0; i < a.length; i++) {
            ans[i * 2] = a[i];
        }
        for (int i = 0; i < b.length; i++) {
            ans[i * 2 + 1] = b[i];
        }
        System.out.println(ans);
    }
}


class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");

    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}