import java.io.*;
import java.util.*;
 
public class Main{
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String word = br.readLine();
        Map<Character, Integer> characterCount = new HashMap<>();
        for (char ch : word.toCharArray()) {
            characterCount.put(ch, characterCount.getOrDefault(ch, 0) + 1);
        }
        StringBuilder sb = new StringBuilder();
        characterCount.entrySet().stream()
                .sorted(Map.Entry.<Character, Integer>comparingByValue().reversed())
                .forEach(record -> {
                    Character key = record.getKey();
                    int value = record.getValue();
                    for(int i = 0; i < value; i++) {
                        sb.append(key);
                    }
                });
        System.out.println(sb);
    }
}

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