#include <bits/stdc++.h>
using namespace std;
using ll = long long;

#ifdef LOCAL
#include <debug.hpp>
#else
#define debug(...)
#endif

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);
    string X, Y;
    cin >> X >> Y;
    if (abs(ssize(X) - ssize(Y)) >= 2) {
        cout << "?" << "\n";
    } else {
        if (ssize(X) < ssize(Y)) swap(X, Y);
        string ans(ssize(X) + ssize(Y), '.');
        for (int i = 0; i < ssize(X); i++) ans[2 * i] = X[i];
        for (int i = 0; i < ssize(Y); i++) ans[2 * i + 1] = Y[i];
        cout << ans << "\n";
    }
}