#include "bits/stdc++.h"
using namespace std;
//諸機能
#pragma region MACRO
#define putans(x) cerr << "answer: "; cout << (x) << endl
#define dputans(x) cerr << "answer: "; cout << setprecision(10) << (x) << endl
#define REP(i, a, n) for (int i = ( a ); i<(int)( n ); i++)
#define RREP(i, a, n) for (int i = (int)( n ); i >= a; i--)
#define rep(i, n) REP(i, 0, n)
#define rrep(i, n) RREP(i, 0, n)
#define ALLOF(a) begin((a)),end((a))
#define FILL(a,n) for(auto &hoge : (a)) hoge = (n)
#define mp(a,b) (make_pair(a,b))
#define exist(container, n) ((container).find((n)) != (container).end())
#define SUBSTR(s,i,l) string((s), (i), (l))
#define NPI_TO_RAD(x) (180.0*x/PI)
#define RAD_TO_NPI(x) (PI/180.0*x)
#pragma endregion
//デバッグなどの支援
#pragma region CODING_SUPPORT
#define dg(var0) { std::cerr << (#var0) << "=" << (var0) << endl; }
#define dgg(var0, var1) { std::cerr << (#var0) << "=" << (var0) << ", ";dg(var1); }
#define dggg(var0, var1, var2) { std::cerr << (#var0) << "=" << (var0) << ", ";dgg(var1,var2); }
#define dgggg(var0, var1, var2, var3) { std::cerr << (#var0) << "=" << (var0) << ", ";dggg(var1,var2,var3); }
#pragma endregion
//typedef（書き換える、書き足す可能性ある）
#pragma region TYPE_DEF
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<string, string> pss;
typedef pair<int, string>pis;
typedef pair<string, int>psi;
typedef vector<string> vs;
typedef vector<int> vi;
#pragma endregion
//諸々の定数(書き換える可能性ある)
#pragma region CONST_VAL
#define PI (2*acos(0.0))
#define EPS (1e-9)
#define MOD (1e9 + 7)
#pragma endregion

int main()
{
	string a, b;
	cin >> a >> b;
	if (a.length() > b.length())
	{
		putans(a); return 0;
	}
	if (b.length() > a.length())
	{
		putans(b); return 0;
	}
	rep(i, a.length())
	{
		int x = a[i] - '0';
		int y = b[i] - '0';
		if (x != y)
		{
			if (x == 4 && y == 7)
			{
				putans(a);
				break;
			}
			if (x == 7 && y == 4)
			{
				putans(b);
				break;
			}
			if (x > y)
			{
				putans(a);
				break;
			}
			else
			{
				putans(b);
				break;
			}
		}
	}
	return 0;
}