importjava.io.BufferedReader;
importjava.io.InputStreamReader;
importjava.io.IOException;
publicclassMain{
    publicstaticvoidmain(String[] args)
    {
        BufferedReader br=newBufferedReader(newInputStreamReader(System.in));
        String str;
        try{
            while((str=br.readLine())!=null)
            {
                System.out.println(count(str).toString());
            }
        }catch(IOException e){
            e.printStackTrace();
        }
    }
    publicstaticStringBuilder count(String str)
    {
        char[] strArray=str.toCharArray();
        int[] chArray=newint[129];
        //字符对应ascll码值下标元素自增来统计数量
        for(chari:strArray)
            chArray[(int)i]++;
        intmax=0;
        //找出字符数量最多的ascll码值
        for(inti=0;i<chArray.length;i++)
            if(max<chArray[i])
                max=chArray[i];
        StringBuilder sb=newStringBuilder();
        //按数量从大到小添加到可变字符序列sb
        while(max!=0)
        {
            for(inti=0;i<chArray.length;i++)
                if(chArray[i]==max)
                    sb.append((char)i);
            max--;
        }
        returnsb;
    }
}