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

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