#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) for(int i = (n) - 1; (i) >= 0; --i)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD LL(1e9 + 7)
#define INF 1000000
using namespace std;
typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PI;

int main() {
	string a, b;
	cin >> a >> b;
	int t1 = a.size();
	int t2 = b.size();
	if (t1 != t2) {
		if (t1 > t2) 
			cout << a << endl;
		else
			cout << b << endl;
		return 0;
	}
	REP(i, t1) {
		if (a[i] == '4' && b[i] == '7' || a[i] == '7' && b[i] == '4') {
			if (a[i] == '4')
				cout << a << endl;
			else
				cout << b << endl;
			return 0;
		}
		else {
			if (a[i] > b[i])
				cout << a << endl;
			else if (a[i] < b[i])
				cout << b << endl;
			else
				continue;
			return 0;
		}
	}
	return 0;
}