import java.io.*;
import java.util.*;
import java.lang.*;

// The "q1" class.
public class Problem4 {
	
    public static void main (String[] args) throws IOException {

	BufferedReader inFile = new BufferedReader (new FileReader ("DATA4.txt"));
	PrintWriter outFile = new PrintWriter (new FileWriter ("OUT4.txt"));
	
	boolean stop = false;
	char output = ' ';
	
	
		for (int count = 1 ; count <= 5 ; count++) {
		    String line = inFile.readLine(), sub = "";
		    for (int i = 0; i < line.length(); i++) {
		    	stop = false;
		    	sub = line.substring(i+1);
		    	for (int check = 0; check < i; check++){
		    		if (line.charAt(i) == line.charAt(check)){
		    			stop = true;
		    			break;
		    		}
		    	}
		    	if ((sub.indexOf(Character.toString(line.charAt(i))) < 0) && (stop == false)) {
		    		outFile.println(line.charAt(i));
		    		break;
		    	}

	    	}
	    	
		}
	inFile.close();
	outFile.close ();




    } // main method
} // q1 class