function HideShow(){
  document.getElementById('hiddenfields_1').style.display = 
    (document.getElementById('hiddenfields_1').style.display == 'none') ? 'block':'none';
    
  document.getElementById('hiddenfields_2').style.display = 
    (document.getElementById('hiddenfields_2').style.display == 'none') ? 'block':'none';
}