#include<iostream>
#include<iomanip>
#include<limits>
#include<stdio.h>
#include<math.h>
#include<algorithm>
#include<queue>
#include<deque>
#include<stack>
#include<string>
#include<string.h>
#include<vector>
#include<set>
#include<map>
#include<bitset>
#include<stdlib.h>
#include<cassert>
#include<time.h>
#include<bitset>
#include<numeric>
#include<unordered_set>
#include<unordered_map>
#include<complex>
using namespace std;
typedef long long ll;
const int mod = 1e9 + 7;
const ll infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;
int main(){
    cout << fixed << setprecision(10);
    string A,B;
    cin >> A >> B;
    int N=A.size(),M=B.size();
    if(N!=M){
        if(N>M)cout << A << endl;
        else cout << B << endl;
    }
    else{
        for(int i=0;i<N;i++){
            if(A[i]==B[i])continue;
            if((A[i]=='4'&&B[i]=='7')){
                cout << A << endl;
            }
            else if(A[i]=='7'&&B[i]=='4'){
                cout << B << endl;
            }
            else if(A[i]>B[i]){
                cout << A << endl;
            }
            else{
                cout << B << endl;
            }
            break;
        }
    }
    return 0;
}