/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		String str = "hello world";
		
		Map<Character, Integer> lettersCount = new HashMap<>();
		
		for (int i=0; i <str.length(); i++) {
			Character current = str.charAt(i);
			if (Character.isLetter(current)) {
				Integer previousCount = lettersCount.get(current);
				if (previousCount != null) {
					lettersCount.put(current, previousCount + 1);
				} else {
					lettersCount.put(current, 1);
				}
			}
		}
		List<Map.Entry<Character, Integer>> list = new LinkedList<Map.Entry<Character, Integer>>( lettersCount.entrySet() );
		Collections.sort( list, new Comparator<Map.Entry<Character, Integer>>()
        {
            public int compare( Map.Entry<Character, Integer> o1, Map.Entry<Character, Integer> o2 )
            {
                return (o2.getValue()).compareTo( o1.getValue() );
            }
        } );
		for (Map.Entry<Character, Integer> entry : list) {
			System.out.println(entry.getKey() + " : " + entry.getValue());
		}
	}
}