#include<bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
template<class T> using V = vector<T>;
template<class T> using VV = V<V<T>>;
template<class T> using VVV = V<VV<T>>;
template<class T> using VVVV = VV<VV<T>>;
#define rep(i,n) for(ll i=0ll;i<n;i++)
#define REP(i,a,n) for(ll i=a;i<n;i++)
const long long INF = (1LL << 60);
const long long mod99 = 998244353;
const long long mod107 = 1000000007;
const long long mod = mod99;
#define eb emplace_back
#define pb eb
#define be(v) (v).begin(),(v).end()
#define all(i,v) for(auto& i : v)
#define all2(i,j,v) for(auto& [i,j] : v)
template<class T, class U> void chmin(T& t, const U& u) { if (t > u) t = u; }
template<class T, class U> void chmax(T& t, const U& u) { if (t < u) t = u; }

// cin.tie(nullptr);
// ios::sync_with_stdio(false);
// cout << fixed << setprecision(20);

void solve(){
  string s,t;
  cin >> s >> t;
  while(s.size()<t.size()) s = "0"+s;
  while(s.size()>t.size()) t = "0"+t;
  ll n = s.size();
  string ans = s;
  VV<ll> v(10, V<ll>(10,0));
  rep(i,10) rep(j,i) v[i][j] = 1;
  v[4][7] = 1;
  v[7][4] = 0;
  rep(i, n) if(s[i]!=t[i]){
  	if(v[s[i]-'0'][t[i]-'0']) break;
  	else{
  		ans = t;
  		break;
  	}
  }
  ll cnt = 0;
  all(c,ans){
  	if(c == '0') cnt++;
  	else break;
  }
  cout << ans.substr(cnt) << endl;
}





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