#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>

#define REP(i,n) for(long (i)=0;(i)<(n);(i)++)
#define FOR(i,a,b) for(long (i)=(a);(i)<(b);(i)++)
#define RREP(i,a) for(long (i)=(a)-1;(i)>=0;(i)--)
#define FORR(i,a,b) for(long (i)=(a)-1;(i)>=(b);(i)--)
#define MOD 1000000007
#define PI acos(-1.0)
#define DEBUG(C) cout<<C<<endl;
#define PII pair<int,int>
#define PLL pair<long,long>
#define ALL(a) (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define RSORT(a) sort((a).begin(),(a).end(),greater<int>())

typedef long long LL;
typedef unsigned long long ULL;

using namespace std;

class myclass{
public:
    void func(){}
};

int main(void){
	string a,b; cin>>a>>b;
	string aa=a,ba=b;
	if(a.size()==b.size()){
		REP(i,a.size()){
			int an=a[i]-'0';
			int bn=b[i]-'0';
			//DEBUG(an)DEBUG(bn)
			if((an==4&&bn==7)||(an==7&&bn==4)){
				if(an<bn){
					cout<<aa<<endl;
					return 0;
				}else if(an>bn){
					cout<<ba<<endl;
					return 0;
				}
			}else{
				if(an>bn){
					cout<<aa<<endl;
					return 0;
				}else if(an<bn){
					cout<<ba<<endl;
					return 0;
				}
			}
		}
	}else if(a.size()>b.size()){
		cout<<aa<<endl;
	}else {
		cout<<ba<<endl;
	}
    return 0;
}