#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS

#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <bitset>
#include <utility>
#include <numeric>
#include <iterator>

using namespace std;

using ll = long long;
using ull = unsigned long long;

const ll inf = 1ll << 60;
const ll mod = (ll)1e9 + 7;

#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()

#define print(s) cout << s;
#define println(s) cout << s << endl;
#define printd(s, f) cout << fixed << setprecision(f) << s << endl;


int main()
{
	string a, b;
	cin >> a >> b;

	if (a.length() > b.length())
	{
		println(a);
	}
	else if (a.length() < b.length())
	{
		println(b);
	}
	else
	{
		for (ll i = 0; i < a.length(); i++)
		{
			if (a[i] == '4' && b[i] == '7')
			{
				println(a);
				return 0;
			}
			else if (a[i] == '7' && b[i] == '4')
			{
				println(b);
				return 0;
			}
			else
			{
				if (a[i] > b[i])
				{
					println(a);
					return 0;
				}
				else if (a[i] < b[i])
				{
					println(b);
					return 0;
				}
			}
		}

		println((stoll(a) > stoll(b) ? a : b));
	}
}