#include<bits/stdc++.h>
using namespace std;
using ll = long long;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    string A, B;
    cin >> A >> B;

    if(A.size()>B.size()){
        p(A);
        return 0;
    }
    else if(A.size()<B.size()){
        p(B);
        return 0;
    }
    else{
        ll L = A.size();
        FOR(i, 0, L){
            if(A[i]==B[i]) continue;

            if(A[i]=='4' && B[i]=='7'){
                p(A);
                return 0;
            }

            if(A[i]=='7' && B[i]=='4'){
                p(B);
                return 0;
            }

            ll a = A[i] - '0';
            ll b = B[i] - '0';
            if(a>b){
                p(A);
                return 0;
            }else{
                p(B);
                return 0;
            }

            
        }
    }
    
    return 0;
}