import java.io.*;

public class dwiteFour {
	
	public static void main(String args[]){
		String word =null;
		int j = 1;
		char unique=' ';
		boolean done = false;
		BufferedReader in = null;
		PrintWriter out = null;
		try{
			in= new BufferedReader(new InputStreamReader(new FileInputStream("DATA4.txt")));
			 out= new PrintWriter(new BufferedWriter(new FileWriter("OUT4.txt")));
		}catch(Exception e){}
		for(int f = 0; f<5; f++){
			try{
				word = in.readLine();
			//	System.out.println(word);
			}catch(Exception e){}
			for(int i=0; i<word.length()-1; i++){
				j=1;
				//done=false;
				try{
					while((word.charAt(i)!= word.charAt(i+j)) && !done){
						
							j++;
						}
				}catch(Exception e){
				//	System.out.println(e);
					unique = word.charAt(i);
					//done=true;
					break;
				}
			}
		out.println(unique);
		}
		out.close();
	}
    
    
}