import java.util.Scanner;
// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
// 注意 hasNext 和 hasNextLine 的区别
String s = in.next();
System.out.println(slove(s));
}
public static StringBuffer slove(String s) {
StringBuffer sb = new StringBuffer(s);
char[] chr = s.toCharArray();
for (int j = 1; j <= chr.length - 1; j++) {
for (int i = 0; i < chr.length - j; i++) {
if (chr[i] == chr[chr.length - j]) {
sb = sb.delete(chr.length - j, chr.length - j + 1);
break;
}
}
}
return sb;
}
}