#include<iostream>
#include<cstdio>
#include<cstring>
#include <cstdlib>  
#include <cmath>   
#include<cctype>
#include<string>
#include<set>
#include<iomanip>
#include <map>
#include<algorithm>
#include <functional>
#include<vector>
#include<climits>
#include<stack>
#include<queue>
#include <deque>
#include <climits>
#include <typeinfo>
#include <utility> 
#define all(x) (x).begin(),(x).end()
#define rep(i,m,n) for(int i = m;i < n;++i)
#define pb push_back
#define fore(i,a) for(auto &i:a)
#define rrep(i,m,n) for(int i = m;i >= n;--i)
#define INF INT_MAX/2
using namespace std;
using ll = long long;
using R = double;
using Data = pair<ll, vector<int>>;
const ll MOD = 1e9 + 7;
const ll inf = 1LL << 50;
struct edge { ll from; ll to; ll cost; };


int prt(string x) {
	cout << x << endl;
	exit(0);
}


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


	if (a.size() > b.size()) {
		cout << a << endl;
	}
	else if(a.size() < b.size()){
		cout << b << endl;
	}
	else {
		rep(i,0,a.size()){
			int dgt1 = a[i] - '0';
			int dgt2 = b[i] - '0';
			if (dgt1 == 7 && dgt2 == 4) {
				prt(b);
			}
			else if (dgt1 == 4 && dgt2 == 7) {
				prt(a);
			}
			else {
				if (dgt1 > dgt2)prt(a);
				else if (dgt1 < dgt2)prt(b);
			}
		}
	}
	

	return 0;
}