#include <iostream>
#include <string>
using namespace std;

int main() {
    string x, y;
    cin >> x >> y;

    if (x.length() < y.length() || x.length() > y.length() + 1) {
        cout << "?" << endl;
    } else {
        string result = "";
        for (size_t i = 0; i < max(x.length(), y.length()); ++i) {
            if (i < x.length()) result += x[i];
            if (i < y.length()) result += y[i];
        }
        cout << result << endl;
    }

    return 0;
}