#include <bits/stdc++.h>
using namespace std;

#define lp(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep(i, n) lp(i, 0, n)
#define rlp(i, a, b) for (int i = (int)(b) - 1; i >= (int)(a); i--)
#define rrep(i, n) rlp(i, 0, n)

#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define all(c) begin(c), end(c)

typedef long long ll;
typedef unsigned long long ull;

template<typename T>
inline void unique(T &c){
	sort(all(c));
	c.erase(unique(all(c)), end(c));
}

int cv[256];
ll calc(string s){
	ll r = 0;
	for (auto c : s) r = r * 10 + cv[c];
	return r;
}

int main()
{
	rep(i, 10) cv[i + '0'] = i;
	swap(cv['4'], cv['7']);

	string s, t;
	cin >> s >> t;

	if (calc(s) < calc(t)) cout << t << endl;
	else cout << s << endl;
}