Input : Geeks for geeks
Output :Gfg
        
Input : United Kingdom
Output : UK

\b[a-zA-Z]

// Java program to demonstrate extracting first
// letter of each word using Regex
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Test
{
	static void printFirst(String s)
	{
		Pattern p = Pattern.compile("\\b[a-zA-Z]");
		Matcher m = p.matcher(s);

		while (m.find())
			System.out.print(m.group());

		System.out.println();
	}

	public static void main(String[] args)
	{
		String s1 = "Geeks for Geeks";
		String s2 = "A Computer Science Portal for Geeks";
		printFirst(s1);
		printFirst(s2);
	}
}

Output:

GfG
ACSPfG