public class MissingLetters
{
	public String getMissingLetters(String sentence)
	{
		boolean occurances[] = new boolean[26];
	
		for(int i = 0; i < sentence.length(); i++)
		{
			int c = (int)sentence.charAt(i);
			
			if(c >= 'A' && c <= 'Z')
				occurances[c-'A'] = true;
			else if(c >= ('A'+32) && c <= ('Z'+32))
				occurances[c-'A'-32] = true;
		}
		
		StringBuilder missing = new StringBuilder();
		
		for(int i = 0; i < occurances.length; i++)
			if(!occurances[i])
				missing.append((char)(i+'A'+32));
		
		return missing.toString();
	}
	
	public static void main(String s[])
	{
		MissingLetters ml = new MissingLetters();
		System.out.println(ml.getMissingLetters("A quick brown fox jumps over the lazy dog"));
		System.out.println(ml.getMissingLetters("A slow yellow fox crawls under the proactive dog"));
		System.out.println(ml.getMissingLetters("Lions, and tigers, and bears, oh my!"));
		System.out.println(ml.getMissingLetters(""));
	}
}