function change(n)
 {
  if(n==1)
  {
   table1.style.display="block";
   td1.className="top";
   table2.style.display="none";
   td2.className="top1";
   table3.style.display="none";
   td3.className="top1";   
   table4.style.display="none";
   td4.className="top1";
  }
  if(n==2)
  {
   table1.style.display="none";
   td1.className="top1";
   table2.style.display="block";
   td2.className="top";
   table3.style.display="none";
   td3.className="top1";   
   table4.style.display="none";
   td4.className="top1";
  }
  if(n==3)
  {
   table1.style.display="none";
   td1.className="top1";
   table2.style.display="none";
   td2.className="top1";
   table3.style.display="block";
   td3.className="top";   
   table4.style.display="none";
   td4.className="top1";
  }
  if(n==4)
  {
   table1.style.display="none";
   td1.className="top1";
   table2.style.display="none";
   td2.className="top1";
   table3.style.display="none";
   td3.className="top1";   
   table4.style.display="block";
   td4.className="top";
  }
 }