#define _CRT_SECURE_NO_WARNINGS
// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
// #define int ll
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
#define all(c) begin(c), end(c)
#define range(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) range(i,0,b)
#define rangei(i,a,b) for(ll a=a;i<=ll(b);i++)
#define repi(i,b) rangei(i,1,b)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
template<class T> ostream & operator << (ostream &os, vector<T> const &);
template<int n, class...T>
typename enable_if<(n>=sizeof...(T))>::type
_ot(ostream &, tuple<T...> const &){}
template<int n, class...T>
typename enable_if<(n< sizeof...(T))>::type
_ot(ostream &os, tuple<T...> const &t){
    os << (n==0?"":" ") << get<n>(t); _ot<n+1>(os, t);
}
template<class...T>
ostream & operator << (ostream &os, tuple<T...> const &t){
    _ot<0>(os, t); return os;
}
template<class T, class U>
ostream & operator<<(ostream &os, pair<T,U> const &p){
    return os << "(" << p.first << ", " << p.second << ") ";
}
template<class T>
ostream & operator<<(ostream &os, vector<T> const &v){
    rep(i,v.size()) os << v[i] << (i+1==(int)v.size()?"":" "); return os;
}
#ifdef DEBUG
#define dump(...) (cerr << #__VA_ARGS__ << " = " << mt(__VA_ARGS__) \
                   << " [" << __LINE__ << "]" << endl)
#else
#define dump(...)
#endif
void fastios(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    // #define endl '\n'
}
template<class T>
size_t uniq(vector<T> &v){
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    return v.size();
}
template<class T>
size_t uniq(T *l, size_t n){
    sort(l,l+n);
    return unique(l,l+n) - l;
}
#define mems(arr,val) memset(arr,val,sizeof(arr));
int const mod = 1000000007;
int const inf = numeric_limits<int>::max()/8;

// ll conv(string s){
//     ll x = 0;
//     rep(i,s.size()) x = x*10 + (s[i]-'0');
//     return x;
// }

// string swap(string s){
//     rep(i,s.size()){
//         if(s[i] == '4') s[i] = '7';
//         else if(s[i] == '7') s[i] = '4';
//     }
//     return s;
// }

// signed main(){
//     string s,t;
//     while(cin >> s >> t){
//         ll a = conv(swap(s));
//         ll b = conv(swap(t));
//         cout << (a > b ? s : t) << endl;
//     }
// }

bool op(string s, string t){
    int n = s.size();
    rep(i,n){
        if(s[i]-t[i]){
            if((s[i] == '4' || s[i] == '7') && (t[i] == '4' || t[i] == '7')) return s[i] > t[i];
            return s[i] < t[i];
        }
    }
    return false;
}

int main(){
    string s,t;
    while(cin >> s >> t){
        if(s.size() == t.size()){
            cout << (op(s,t) ? t : s) << endl;
        } else {
            cout << (s.size() < t.size() ? t : s) << endl;
        }
    }
}