#include <vector>
#include <iostream>
#include <string>
#include <ostream>
#include <map>
#include <set>
#include <bitset>
#include <cmath>
#include <iomanip>
#include <algorithm>
#include <list>
#define rep(i, n) for (int i = 0; i < (n); i++)
using namespace std;

int main()
{
    string x, y;
    cin >> x >> y;
    if(x.size() - y.size() == 0 || x.size() - y.size() == 1){
        for(int i=0;i<x.size()+y.size();i++){
            if(i%2==0)cout << x[i/2];
            else cout << y[i/2];
        }
    }else cout << "?";
}