import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.PrintWriter; import java.util.StringTokenizer; public class Main { static BufferedReader in; static PrintWriter out; static StringTokenizer tok; void solve() throws IOException { String a = ns(); String b = ns(); if (a.length() < b.length()) { out.println(b); return; } if (b.length() < a.length()) { out.println(a); return; } int[] digitsa = a.chars().map(c -> c - '0').toArray(); int[] digitsb = b.chars().map(c -> c - '0').toArray(); for (int i = 0; i < a.length(); i++) { if (digitsa[i] != digitsb[i]) { if (digitsa[i] == 4 && digitsb[i] == 7) { out.println(a); return; } else if (digitsa[i] == 7 && digitsb[i] == 4) { out.println(b); return; } else { out.println(digitsa[i] < digitsb[i] ? b : a); } } } } String ns() throws IOException { while (!tok.hasMoreTokens()) { tok = new StringTokenizer(in.readLine(), " "); } return tok.nextToken(); } int ni() throws IOException { return Integer.parseInt(ns()); } long nl() throws IOException { return Long.parseLong(ns()); } double nd() throws IOException { return Double.parseDouble(ns()); } String[] nsa(int n) throws IOException { String[] res = new String[n]; for (int i = 0; i < n; i++) { res[i] = ns(); } return res; } int[] nia(int n) throws IOException { int[] res = new int[n]; for (int i = 0; i < n; i++) { res[i] = ni(); } return res; } long[] nla(int n) throws IOException { long[] res = new long[n]; for (int i = 0; i < n; i++) { res[i] = nl(); } return res; } public static void main(String[] args) throws IOException { in = new BufferedReader(new InputStreamReader(System.in)); out = new PrintWriter(System.out); tok = new StringTokenizer(""); Main main = new Main(); main.solve(); out.close(); } }