#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    string A,B; cin >> A >> B;
    if(A.size() > B.size()) {
        cout << A << endl;
    } else if(A.size() < B.size()) {
        cout << B << endl;
    } else {
        int n = A.size();
        for(int i = 0; i < n; i++) {
            if(A[i] != B[i]) {
                if(A[i] == '4' && B[i] == '7')
                    cout << A << endl;
                else if(A[i] == '7' && B[i] == '4')
                    cout << B << endl;
                else {
                    if(A[i] > B[i]) 
                        cout << A << endl;
                    else
                        cout << B << endl;
                }
                return 0;
            }
        }

        cout << A << endl;
    }
}