#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cctype>
#include<cstdlib>
#include<algorithm>
#include<bitset>
#include<vector>
#include<list>
#include<deque>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<cmath>
#include<sstream>
#include<fstream>
#include<iomanip>
#include<ctime>
#include<complex>
#include<functional>
#include<climits>
#include<cassert>
#include<iterator>
#include<unordered_set>
#include<unordered_map>
using namespace std;
string s;
string t;
int main() {
	cin >> s;
	cin >> t;
	if (s.size() != t.size()) {
		if (s.size() > t.size()) {
			cout << s << endl;
		}
		else {
			cout << t << endl;
		}
		return 0;
	}
	for (int i = 0;i < s.size();i++) {
		if (s[i] == '4'&&t[i] == '7') {
			cout << s << endl;
			return 0;
		}
		if (s[i] == '7'&&t[i] == '4') {
			cout << t << endl;
			return 0;
		}
		if (s[i] > t[i]) {
			cout << s << endl;
			return 0;
		}
		if (s[i] < t[i]) {
			cout << t << endl;
			return 0;
		}
	}
	cout << s << endl;
	return 0;
}