#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    string s, t;
    cin >> s >> t;
    int n = s.size();
    int m = t.size();
    if(n > m){
        cout << s << endl;
    }else if(n < m){
        cout << t << endl;
    }else{
        int i = 0;
        while(s[i] == t[i])i++;
        if(s[i] == '4' && t[i] == '7'){
            cout << s << endl;
        }else if(s[i] == '7' && t[i] == '4'){
            cout << t << endl;
        }else if(s[i] > t[i]){
            cout << s << endl;
        }else{
            cout << t << endl;
        }
    }
    return 0;
}