import java.util.*;
import java.io.*;
import java.awt.geom.*;
import java.math.*;

public class No0292 {

	static final Scanner in = new Scanner(System.in);
	static final PrintWriter out = new PrintWriter(System.out,false);

	static void solve() {
		String a = in.next();
		String b = in.next();
		int n = a.length();
		int m = b.length();

		if (n != m) {
			out.println(n > m ? a : b);
			return;
		}

		for (int i=0; i<n; i++) {
			if (a.charAt(i) != b.charAt(i)) {
				if ((a.charAt(i) == '4' || a.charAt(i) == '7') && (b.charAt(i) == '4' || b.charAt(i) == '7'))
					out.println(a.charAt(i) == '4' ? a : b);
				else
					out.println(a.charAt(i) > b.charAt(i) ? a : b);
				return;
			}
		}
	}

	public static void main(String[] args) {
		long start = System.currentTimeMillis();

		solve();
		out.flush();

		long end = System.currentTimeMillis();
		//trace(end-start + "ms");
		in.close();
		out.close();
	}

	static void trace(Object... o) { System.out.println(Arrays.deepToString(o));}
}