#include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <array>
#include <deque>
#include <forward_list>	
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <string>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <functional>
#include <queue>
#include <stack>
#include <cmath>
#include <iomanip>
#include <list>
#include <tuple>
#include <bitset>
#include <ciso646>
#include <fstream>
#include <random>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> T;
#define vec vector<ll>
#define vec2 vector<vec>
#define vec3 vector<vec2>

#define For(i,a,b)	for(ll (i) = (a);i < (b);(i)++)
#define rep(i,n)	For(i,0,n)
#define rFor(i,a,b)	for(ll (i) = (a-1);i >= (b);(i)--)
#define rrep(i,n)	rFor(i,n,0)
#define each(i,a)	for(auto i : a)
#define clr(a)		memset((a), 0 ,sizeof(a))
#define mclr(a)		memset((a), -1 ,sizeof(a))
#define all(a)		(a).begin(),(a).end()
#define sz(a)		(sizeof(a))
#define toint toInt
#define tostr toString

const int dx[8] = { 1, 0, -1, 0, 1, 1, -1, -1 }, dy[8] = { 0, -1, 0, 1, -1, 1, -1, 1 };
const int mod = 1000000007;
const int INF = 1e9 + 2;
template<class T> inline T sqr(T x) { return x*x; }
template<class T> inline T mypow(T x, ll n){ T res = 1; while (n > 0){ if (n & 1)res = res * x;	x = x * x;	n >>= 1; }return res; }
inline int gcd(ll a, ll b){ return b ? gcd(b, a%b) : a; }
inline int lcm(ll a, ll b){ return a / gcd(a, b) * b; }
inline bool cheak(int x, int y, int xMax, int yMax){ return x >= 0 && y >= 0 && xMax > x && yMax > y; }
inline ll toInt(string s) { ll v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
template<class _RanIt>	inline	string toString(_RanIt _First, _RanIt _Last, string sep)				{ if (_First == _Last)return ""; ostringstream sout; sout << *_First; for (_First = next(_First); _First != _Last; _First = next(_First)) { sout << sep << *_First; }return sout.str(); }
template<class _RanIt>	inline	string toString(_RanIt _First, _RanIt _Last, string sep, string sep2)	{ if (_First == _Last)return ""; ostringstream sout; sout << toString(all(*_First), sep); for (_First = next(_First); _First != _Last; _First = next(_First)) { sout << sep2 << toString(all(*_First), sep); }return sout.str(); }


int main(){

	string a, b;
	cin >> a >> b;
	
	if (a.size() > b.size()){
		cout << a << endl; return 0;
	}
	if (b.size() > a.size()){
		cout << b << endl; return 0;
	}

	rep(i, a.size()){
		if (a[i] == '4' && b[i] == '7'){
			cout << a << endl; return 0;
		}
		if (a[i] == '7' && b[i] == '4'){
			cout << b << endl; return 0;
		}
		if (a[i] > b[i]){
			cout << a << endl; return 0;
		}
		else{
			cout << b << endl; return 0;
		}
	}

	return 0;
}