/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
 
/* 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
	{
final String regex = "^(#{1,6}\\s*[\\S]+)";
final String string = "#heading 1 \n"
	 + "bla bla bla\n"
	 + "### heading 3 djdjdj\n"
	 + "bla bla bla\n"
	 + "## heading 2 bal;kasddfas\n"
	 + "fbla bla bla";
final String subst = "<b>$1</b>";
 
final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
final Matcher matcher = pattern.matcher(string);
 
// The substituted value will be contained in the result variable
final String result = matcher.replaceAll(subst);
 
System.out.println("Substitution result: " + result);		
	}
}

LyogcGFja2FnZSB3aGF0ZXZlcjsgLy8gZG9uJ3QgcGxhY2UgcGFja2FnZSBuYW1lISAqLwoKaW1wb3J0IGphdmEudXRpbC4qOwppbXBvcnQgamF2YS5sYW5nLio7CmltcG9ydCBqYXZhLmlvLio7CmltcG9ydCBqYXZhLnV0aWwucmVnZXguTWF0Y2hlcjsKaW1wb3J0IGphdmEudXRpbC5yZWdleC5QYXR0ZXJuOwoKCi8qIE5hbWUgb2YgdGhlIGNsYXNzIGhhcyB0byBiZSAiTWFpbiIgb25seSBpZiB0aGUgY2xhc3MgaXMgcHVibGljLiAqLwpjbGFzcyBJZGVvbmUKewoJcHVibGljIHN0YXRpYyB2b2lkIG1haW4gKFN0cmluZ1tdIGFyZ3MpIHRocm93cyBqYXZhLmxhbmcuRXhjZXB0aW9uCgl7CmZpbmFsIFN0cmluZyByZWdleCA9ICJeKCN7MSw2fVxccypbXFxTXSspIjsKZmluYWwgU3RyaW5nIHN0cmluZyA9ICIjaGVhZGluZyAxIFxuIgoJICsgImJsYSBibGEgYmxhXG4iCgkgKyAiIyMjIGhlYWRpbmcgMyBkamRqZGpcbiIKCSArICJibGEgYmxhIGJsYVxuIgoJICsgIiMjIGhlYWRpbmcgMiBiYWw7a2FzZGRmYXNcbiIKCSArICJmYmxhIGJsYSBibGEiOwpmaW5hbCBTdHJpbmcgc3Vic3QgPSAiPGI+JDE8L2I+IjsKCmZpbmFsIFBhdHRlcm4gcGF0dGVybiA9IFBhdHRlcm4uY29tcGlsZShyZWdleCwgUGF0dGVybi5NVUxUSUxJTkUpOwpmaW5hbCBNYXRjaGVyIG1hdGNoZXIgPSBwYXR0ZXJuLm1hdGNoZXIoc3RyaW5nKTsKCi8vIFRoZSBzdWJzdGl0dXRlZCB2YWx1ZSB3aWxsIGJlIGNvbnRhaW5lZCBpbiB0aGUgcmVzdWx0IHZhcmlhYmxlCmZpbmFsIFN0cmluZyByZXN1bHQgPSBtYXRjaGVyLnJlcGxhY2VBbGwoc3Vic3QpOwoKU3lzdGVtLm91dC5wcmludGxuKCJTdWJzdGl0dXRpb24gcmVzdWx0OiAiICsgcmVzdWx0KTsJCQoJfQp9