#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

void arrange(string& a, string& b) {
	reverse(ALL(a));
	reverse(ALL(b));
	
	int ma = max(a.size(), b.size());
	
	while (a.size() < ma) a += "0";
	while (b.size() < ma) b += "0";
	
	reverse(ALL(a));
	reverse(ALL(b));
}

int main() {
	string a, b;
	cin >> a >> b;
	
	string ta = a, tb = b;
	arrange(ta, tb);
	
	bool gr = false;
	REP(i, ta.size()) {
		if (ta[i] == '4' && tb[i] == '7') break;
		if (ta[i] == '7' && tb[i] == '4') { gr = true; break; }
		
		if (ta[i] < tb[i]) { gr = true; break; }
		if (ta[i] > tb[i]) break;
	}
	
	cout << (gr ? b : a) << endl;
	
	return 0;
}