#include <bits/stdc++.h>

using namespace std;

int main() {
  string A, B;
  cin >> A >> B;
  if (A.size() > B.size()) {
    cout << A << endl;
  } else if (B.size() > A.size()) {
    cout << B << endl;
  } else {
    for (size_t i = 0; i < A.size(); ++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;
      }
      return 0;
    }
    cout << A << endl;
  }
  return 0;
}