#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<vector>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<utility>
#include<sstream>
#include<cctype>
#include<cmath>
#include<algorithm>
using namespace std;

#define ALL(x) (x).begin(),(x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define rev(i,n) for(int (i)=(n-1);(i)>=0;(i)--)
#define repp(i,n) for(int (i)=1;(i)<=(n);(i)++)
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rev(i,n) for(int (i)=(n-1);(i)>=0;(i)--)
#define clr(a) memset((a), 0 ,sizeof(a))


typedef pair<int,int> P;
typedef vector<pair<int,int> > pii;
typedef map<string,int> mi;


int main(){
	string s,s2;
	cin >> s >> s2;
	if(s.size()>s2.size()) cout << s << endl;
	else if(s.size()<s2.size()) cout << s2 << endl;
	else{
		for(int i=0;i<s.size();i++){
			if(s[i]>s2[i]){
				if(s[i]=='7'&&s2[i]=='4')
					cout << s2 << endl;
				else
					cout << s << endl;
				return 0;
			}
			if(s[i]<s2[i]){
				if(s[i]=='4'&&s2[i]=='7')
					cout << s << endl;
				else
					cout << s2 << endl;
				return 0;
			}
		}
	}
	return 0;
}