#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  string A, B;
  cin >> A >> B;
  if (A.size() < B.size()) {
    cout << B << '\n';
  } else if (A.size() > B.size()) {
    cout << A << '\n';
  } else {
    for (int i = 0; i < (int)A.size(); i++) {
      if (A[i] != B[i]) {
        if ((A[i] == '4' || A[i] == '7') && (B[i] == '4' || B[i] == '7')) {
          if (A[i] == '4') {
            cout << A << '\n';
          } else {
            cout << B << '\n';
          }
        } else {
          cout << (A[i] < B[i] ? B : A) << '\n';
        }
        break;
      }
    }
  }
  return 0;
}