#include<bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;

#define all(v) v.begin(),v.end()
using ll = long long;
using ull = unsigned long long;
using lll = __int128;
using vll=vector<ll>;
using vvll = vector<vector<ll>>;
using P = pair<ll,ll>;
using vp=vector<pair<ll, ll>>;
//using mint=modint1000000007;
//using mint=modint998244353;

const ll INF=1ll<<60;
ll mod10=1e9+7;
ll mod99=998244353;
const double PI = acos(-1);

#define rep(i,n) for (ll i=0;i<n;++i)
#define per(i,n) for(ll i=n-1;i>=0;--i)
#define rep2(i,a,n) for (ll i=a;i<n;++i)
#define per2(i,a,n) for (ll i=a;i>=n;--i)

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }

bool solve(){
   string S,T;cin>>S>>T;
   ll N=S.size(),M=T.size();
   if(!(N==M||N-1==M)){
      cout << "?" << endl;
      return 0;
   }
   rep(i,M) cout<<S[i]<<T[i];
   if(N-1==M) cout<<S.back();
   cout  << endl;
   return 0;
}




int main(){
   cin.tie(0);
   ios::sync_with_stdio(false);
   ll T=1;//cin>>T;
   rep(i,T) solve();
}