#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000000
#define Inf64 1000000000000000001LL

int main(){
	
	string S,T;
	cin>>S>>T;
	int n = S.size(),m = T.size();
	string ans(n+m,'a');
	rep(i,n+m){
		int c = i/2;
		if(i%2==0){
			if(c >= n){
				ans = "?";
				break;
			}
			else ans[i] = S[c];
		}
		else{
			if(c >= m){
				ans = "?";
				break;
			}
			else ans[i] = T[c];
		}
	}
	cout<<ans<<endl;
	
	return 0;
}