#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1e9 + 10;
const ll INFL = 4e18;

int main() {
    string X, Y;
    cin >> X >> Y;

    int d = ssize(X) - ssize(Y);

    if (d == 0) {
        for (int i = 0; i < ssize(X); i++) cout << X[i] << Y[i];
        cout << endl;
    } else if (d == 1) {
        cout << X[0];
        for (int i = 1; i < ssize(X); i++) cout << Y[i - 1] << X[i];
        cout << endl;
    } else {
        cout << "?" << endl;
    }
}