#include <iostream>
#include <cstdio>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <math.h>
#include <map>
#include <functional>
#include <iomanip>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <typeinfo>
#define PI 3.14159265359
#define INF 99999999
#define rep(i, n) for(int i=0; i<n; i++)
#define REP(n) rep(i, n)
#define EPS 1e-10
#define pb push_back
#define mp make_pair
typedef long long ll;
using namespace std;
typedef pair<int, int> P;


int main()
{
	string A, B;
	
	cin >> A >> B;
	if (A.length() > B.length())
	{
		cout << A << endl;
	} else if (A.length() < B.length()) {
		cout << B << endl;
	} else {
		//同じ長さだった場合
		for (int i=0; i<A.length(); i++)
		{
			if ((A[i] == '4' || A[i] == '7') && (B[i] == '4' || B[i] == '7') && (A[i] != B[i]))
			{
				if (A[i] > B[i]) cout << B << endl;
				else cout << A << endl;
				break;
			} else if (A[i] != B[i]) {
				if (A[i] > B[i])
				{
					cout << A << endl;
				} else {
					cout << B << endl;
				}
				break;
			}
		}
	}
	
	return 0;
}