function GetWidth()
{ 
  var x = 0;
  if (self.innerHeight)
  {
 x = self.innerWidth;
  }
  else if (document.documentElement && document.documentElement.clientHeight)
  { 
 x = document.documentElement.clientWidth;
  }
  else if (document.body)
  {
 x = document.body.clientWidth;
  }
  return x;
}
  
 
  
function GetHeight()
{
  var y = 0;
  if (self.innerHeight)
  {
 y = self.innerHeight;
  }
  else if (document.documentElement && document.documentElement.clientHeight)
	{ 
 y = document.documentElement.clientHeight;
  }
  else if (document.body) 
  {
 y = document.body.clientHeight;
  }
  return y;

}
function canviar(){
	  var ampl=GetWidth();
	  var alc=GetHeight();
	  var canvi=(ampl-1000)/2;
	  window.document.getElementById('amplada').style.width=canvi;
}