import java.util.*;
import java.lang.*;
import java.io.*;
public class Main
{
{
Scanner in
= new Scanner
(System.
in); int n = in.nextInt();
char res = 0;
for(int i = 0; i < n; i++)
res ^= s.charAt(i);
if (res == 0)
else
System.
out.
printf("%c\n",res
); }
}
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