#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <string>
#include <queue>
#include <stack>
#include <math.h>
#include <set>
#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define P pair<int, int>

#define MOD 1000000007
#define INF 1012345678
#define NINF (-2147483647-1)
#define LLINF 9223372036854775807
using ll = long long;
using namespace std;

int main() {
    string s, t;
    cin >> s >> t;
    if (s.length() > t.length()) {
        cout << s << endl;
    }
    else if (s.length() < t.length()){
        cout << t << endl;
    }
    else {
        for (int i = 0; i < s.length(); i++)
        {
            if (s[i] != t[i]) {
                if (s[i] == '4' && t[i] == '7') {
                    cout << s << endl;
                }
                else if (s[i] == '7' && t[i] == '4'){
                    cout << t << endl;
                }
                else {
                    cout << ((s[i] > t[i]) ? s : t) << endl;
                }
                break;
            }
        }
    }
    getchar(); getchar();
    return 0;
}