#include <bits/stdc++.h>
#include <atcoder/all>

using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
static const double pi = 3.141592653589793;
const ll INF = 1LL << 60;
const ll mod = 1000000007;
const ll imod = 998244353;
using mint = modint998244353;
vector<int> dx = {1, 0, -1, 0}, dy = {0, 1, 0, -1};
ll P(ll x, ll n) {
  ll ret = 1;
    while (n > 0) {
      if (n & 1) ret *= x;
      x *= x;
      n >>= 1;
  }
  return ret;
}

void seek(bool f){
  cout << (f ? "Yes" : "No") << endl;
}

int main(){
	string X, Y;
	cin >> X >> Y;
	if(abs((int)X.size() - (int)Y.size()) > 1 or X.size() < Y.size()){
		cout << "?" << endl;
	}
	else{
		int x = 0, y = 0;
		rep(i, X.size() + Y.size()){
			if(i % 2 == 0){
				cout << X[x];
				x++;
			}
			else{
				cout << Y[y];
				y++;
			}
		}
	}
}