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package com.javarush.task.task18.task1804;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import static java.lang.Character.MAX_VALUE;
/*
Самые редкие байты
*/
public class Solution {
public static void main(String[] args) throws Exception {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String str = reader.readLine();
ArrayList<Integer> mainlist = new ArrayList<>();
HashMap<Integer,Integer> map = new HashMap<>();
FileInputStream in = new FileInputStream(str);
while (in.available()>0){
mainlist.add(in.read());
}
int count=0;
for(int i =0;i<mainlist.size()-1;i++){
count= Collections.frequency(mainlist,mainlist.get(i));
map.put(mainlist.get(i),count);
}
if(!map.isEmpty()){
int min= Collections.min(map.values());{
for(Map.Entry<Integer,Integer> du:map.entrySet()){
if(du.getValue()==min){
System.out.print(du.getKey()+" ");
}
}
in.close();
}
}
}
}