#include <bits/stdc++.h>
#define rep(i,n) for(int i=(0);i<(n);i++)

using namespace std;

typedef long long ll;

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }

ll s2i(string s){
	ll ret = 0;
	int n = s.size();
	rep(i, n){
		ret *= 10;
		ll d = s[i] - '0';
		ll dd = d;
		if(d == 4) dd = 7;
		if(d == 7) dd = 4;

		ret += dd;
	}

	return ret;
}

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	string a, b;
	cin >> a >> b;

	ll ia = s2i(a), ib = s2i(b);

	if(ia > ib){
		cout << a << endl;
	}else{
		cout << b << endl;
	}
}