#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef string str;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    str s1, s2;
    cin >> s1 >> s2;
    if (s1.size() == s2.size() || s1.size() == s2.size() + 1)
    {
        ll i = 0;
        while (i < s1.size())
        {
            if (i < s1.size()) cout << s1[i];
            if (i < s2.size()) cout << s2[i];
            i++;
        }
    }
    else cout << '?';
    return 0;
}