#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

bool solve(const string& a, const string& b)
{
    if(a.size() != b.size())
        return a.size() < b.size();

    for(unsigned i=0; i<a.size(); ++i){
        if(a[i] != b[i]){
            if(min(a[i], b[i]) == '4' && max(a[i], b[i]) == '7')
                return a[i] == '7';
            else
                return a[i] < b[i];
        }
    }

    return false;
}

int main()
{
    string a, b;
    cin >> a >> b;

    if(solve(a, b))
        cout << b << endl;
    else
        cout << a << endl;

    return 0;
}