function countChars(textbox, counter, max) {
  var count = max - document.getElementById(textbox).value.length;

  if (count < 0) { 
	
	document.getElementById(counter).innerHTML = "<span class=\"extension_counter\">" + "Letters in long part: " + Math.abs(count) + "</span>";
	
	} else {
	
	document.getElementById(counter).innerHTML = "<span class=\"sms_counter\">" + "Letters left for SMS part: " + count + "</span>"; 
	
	}
	
}