import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) {
	      BufferedReader stdReader =new BufferedReader(new InputStreamReader(System.in));
	      try {
	    	  String[] temp = stdReader.readLine().split(" ");
	    	  if(temp[0].length() > temp[1].length()){
	    		  System.out.println(temp[0]);
	    	  }else if(temp[0].length() < temp[1].length()){
	    		  System.out.println(temp[1]);
	    	  }else{
	    		  for(int i=0;i<temp[0].length();i++){
	    			  if(temp[0].charAt(i) != temp[1].charAt(i)){
	    				  if(temp[0].charAt(i)=='4'&& temp[1].charAt(i)=='7'){
	    		    		  System.out.println(temp[0]);
	    				  }else if(temp[0].charAt(i)=='7' && temp[1].charAt(i)=='4'){
	    					  System.out.println(temp[1]);
	    				  }else if(temp[0].charAt(i) > temp[1].charAt(i)){
	    		    		  System.out.println(temp[0]);
	    				  }else{
	    					  System.out.println(temp[1]);
	    				  }
	    				  break;
	    			  }
	    		  }
	    	  }
	      } catch (IOException e) {
			e.printStackTrace();
	      }
	}
}