#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

int main() {
    
    string A,B;
    cin >> A >> B;
    if ( A.length() > B.length() ) { cout << A << endl; return 0; }
    if ( A.length() < B.length() ) { cout << B << endl; return 0; }

    for ( int i = 0; i < A.length(); i++ ) {
        int a = A[i]-'0';
        int b = B[i]-'0';
        if ( a == b ) { continue; }
        bool f = a > b;
        if ( a == 7 && b == 4 ) { f = false; }
        if ( a == 4 && b == 7 ) { f = true; }
        cout << ( f ? A : B ) << endl;
        break;
    }

    return 0;
}