using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var x = ReadLine();
        var y = ReadLine();
        var c = new char[x.Length + y.Length];
        if (x.Length == y.Length)
        {
            for (var i = 0; i < x.Length; ++i)
            {
                c[i * 2] = x[i];
                c[i * 2 + 1] = y[i];
            }
        }
        else if (x.Length == y.Length + 1)
        {
            for (var i = 0; i < y.Length; ++i)
            {
                c[i * 2] = x[i];
                c[i * 2 + 1] = y[i];
            }
            c[^1] = x[^1];
        }
        else
        {
            WriteLine("?");
            return;
        }
        WriteLine(string.Concat(c));
    }
}