function chgtt(i)
 {
    if(i==1)
 {
   book1.style.display="";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display="none"; 
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
}
 else
 if(i==2)
 {
   book1.style.display="none";
   book2.style.display="";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display="none";
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
 }
 else
 if(i==3)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display="none";
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
 }
else
    if(i==4)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display="none"; 
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
}
 else
 if(i==5)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="";
   bk3.style.display="none";
   bk4.style.display="none"; 
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
}
 else
 if(i==6)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="";
   bk4.style.display="none"; 
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
}
 else
 if(i==7)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display=""; 
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
 }
 else
 if(i==8)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display="none"; 
   bk5.style.display=""; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
 }
 else
 if(i==9)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display="none"; 
   bk5.style.display="none"; 
   bk6.style.display="";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
 }
 else
 if(i==10)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display="none"; 
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="";
   bk8.style.display="none";
   bk9.style.display="none";
   book.style.display="none";
 }
 else
 if(i==11)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display="none"; 
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="";
   bk9.style.display="none";
   book.style.display="none";
 }
 else
 if(i==12)
 {
   book1.style.display="none";
   book2.style.display="none";
   book3.style.display="none";
   bk1.style.display="none";
   bk2.style.display="none";
   bk3.style.display="none";
   bk4.style.display="none"; 
   bk5.style.display="none"; 
   bk6.style.display="none";
   bk7.style.display="none";
   bk8.style.display="none";
   bk9.style.display="";
   book.style.display="none";
}
}