#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef complex<double> P;
typedef pair<int,int> pii;
#define REP(i,n) for(ll i=0;i<n;++i)
#define REPR(i,n) for(ll i=1;i<n;++i)
#define FOR(i,a,b) for(ll i=a;i<b;++i)

#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define DEBUG_VEC(v) cout<<#v<<":";REP(i,v.size())cout<<" "<<v[i];cout<<endl
#define ALL(a) (a).begin(),(a).end()

#define MOD (ll)(1e9+7)
#define ADD(a,b) a=((a)+(b))%MOD
#define FIX(a) ((a)%MOD+MOD)%MOD

int main(){
  string a,b;
  cin >> a >> b;
  if(a.size()>b.size()){
    cout << a << endl;
    return 0;
  }else if(a.size()<b.size()){
    cout << b << endl;
    return 0;
  }
  assert(a.size()==b.size());
  ll len = a.size();
  REP(i,len){
    int ca = a[i]-'0';
    int cb = b[i]-'0';
    if((ca==7 && cb==4) || (ca==4 && cb==7)){
      ca = 11-ca;
      cb = 11-cb;
    }
    if(ca>cb){
      cout << a << endl;
      return 0;
    }else if(ca<cb){
      cout << b << endl;
      return 0;
    }
  }
  return 0;
}