#nullable enable

using System.Numerics;

object? Solve()
{
    var x = String();
    var y = String();
    var d = x.Length - y.Length;
    if (d == 0 || d == 1)
    {
        var ans = "";
        for (var i = 0; i < Math.Min(x.Length, y.Length); i++)
        {
            ans += x[i];
            ans += y[i];
        }
        if (d == 1) ans += x[^1];
        return ans;
    }
    return "?";
}

#region
AtCoderIO _io_;
var _backend_ = new StandardIOBackend();
_io_ = new(){ Backend = _backend_ };
Out(Solve());
_backend_.Flush();

string String() => _io_.Next();
int Int() => int.Parse(String());
void Out(object? x, string? sep = null) => _io_.Out(x, sep ?? Environment.NewLine);

class AtCoderIO
{
    public required StandardIOBackend Backend { get; init; }

    Memory<string> _input = Array.Empty<string>();
    int _iter = 0;
    public string Next()
    {
        while (_iter >= _input.Length) (_input, _iter) = (Backend.ReadLine().Trim().Split(' '), 0);
        return _input.Span[_iter++];
    }

    public void Out(object? x, string separator)
    {
        if (x == null) return;
        if (x is System.Collections.IEnumerable a and not string)
        {
            var objects = a.Cast<object>();
            if (!objects.Any()) return;
            x = string.Join(separator, objects);
        }
        Backend.WriteLine(x);
    }
}

class StandardIOBackend
{
    readonly StreamReader _sr = new(Console.OpenStandardInput());
    readonly StreamWriter _sw = new(Console.OpenStandardOutput()) { AutoFlush = false };
    public string ReadLine() => _sr.ReadLine()!;
    public void WriteLine(object? value) => _sw.WriteLine(value);
    public void Flush() => _sw.Flush();
}
#endregion

static class Extensions
{
    public static T[] Repeat<T>(this int time, Func<T> F) => Enumerable.Range(0, time).Select(_ => F()).ToArray();

    public static (long d, long x, long y) ExtendedGCD(long a, long b)
    {
        var (x0, y0, x1, y1) = (1L, 0L, 0L, 1L);
        while (b != 0)
        {
            var q = a / b;
            (a, b) = (b, a - q * b);
            (x0, y0, x1, y1) = (x1, y1, x0 - q * x1, y0 - q * y1);
        }
        return (a, x0, y0);
    }
}