public class Solution {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        FileInputStream inputStream = new FileInputStream(br.readLine());
        int count = 1, max_count = 1;
        ArrayList<Integer> el = new ArrayList<Integer>();
        ArrayList<Integer> list = new ArrayList<Integer>();
        HashSet<Integer> elements = new HashSet<Integer>();
        while (inputStream.available()>0)
        {
        list.add(inputStream.read());
        }
        for (int i=0; i<list.size(); i++)
        {
            count=1;
            for (int j=1; j<list.size(); j++)
            {
                if (list.get(i)==list.get(j))
                    count++;
            }
            if (count>max_count){
                max_count=count;
                }

        }
        for (int i=0; i<list.size(); i++)
        {
            count=1;
            for (int j=1; j<list.size(); j++)
            {

                if (list.get(i)==list.get(j))
                    count++;
            }
            if (count==max_count)
        {
            elements.add(list.get(i));
        }
        for (int i=0; i<elements.toArray().length; i++)
            System.out.print(elements.toArray()[i]+" ");


        inputStream.close();
    }
}