#include <bits/stdc++.h>

using namespace std;

void fast_io() {
	ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
}

int main() {
	fast_io();
	string x, y;
	cin >> x >> y;
	if (x.size() == y.size()) {
		int n = x.size();
		for (int i = 0; i < n; i++) {
			cout << x[i] << y[i];
		}
		cout << endl;
	} else if (x.size() == y.size() + 1) {
		int n = y.size();
		for (int i = 0; i < n; i++) {
			cout << x[i] << y[i];
		}
		cout << x[n] << endl;
	} else {
		cout << "?\n";
	}
}