#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <string.h>

using namespace std;
using ll = long long;

int main(){
    string a , b;
    cin >> a >> b;
    
    if(a.size() > b.size()){
        cout << a << endl;
        exit(0);
    }
    
    if(a.size() < b.size()){
        cout << b << endl;
        exit(0);
    }
    
    if(a == b){
        cout << a << endl;
        exit(0);
    }
    
    int n = a.size();
    for(int i = 0; i < n; i++){
        int aa = a[i] - '0';
        int bb = b[i] - '0';
        if(aa == bb)continue;
        if(aa == 4 && bb == 7){
            cout << a << endl;
            exit(0);
        }
        if(aa == 7 && bb == 4){
            cout << b << endl;
            exit(0);
        }
        if(aa > bb){
            cout << a << endl;
            exit(0);
        }
        if(aa < bb){
            cout << b << endl;
            exit(0);
        }
    }
    return 0;
}