function clean ()
{ //alert(anzahl);
 var layers=document.getElementsByTagName("div");
 for(var a=0;a<anzahl;){
  a=a+2;
  layers[a].style.visibility='hidden';
 }
}

function menu(i)
{
var layers=document.getElementsByTagName("div");
switch(i)
 {
  case (1):
   {
    layers[0].style.visibility='visible';
    layers[2].style.visibility='visible';
    for(var a=2;a<anzahl;){ a=a+2;
     layers[a].style.visibility='hidden';
    }
   break;
   }
  case (2):
   {
    layers[0].style.visibility='visible';
    layers[2].style.visibility='hidden';
    layers[4].style.visibility='visible';
    for(var a=4;a<anzahl;){ a=a+2;
     layers[a].style.visibility='hidden';
    }
   break;
   }
  case (3):
   {
    layers[0].style.visibility='visible';
    layers[2].style.visibility='hidden';
    layers[4].style.visibility='hidden';
    layers[6].style.visibility='visible';
    for(var a=6;a<anzahl;){ a=a+2;
     layers[a].style.visibility='hidden';
    }
   break;
   }
  case (4):
   {
    layers[0].style.visibility='visible';
    layers[2].style.visibility='hidden';
    layers[4].style.visibility='hidden';
    layers[6].style.visibility='hidden';
    layers[8].style.visibility='visible';
    for(var a=8;a<anzahl;){ a=a+2;
     layers[a].style.visibility='hidden';
    }
   break;
   }
  case (5):
   {
    layers[0].style.visibility='visible';
    layers[2].style.visibility='hidden';
    layers[4].style.visibility='hidden';
    layers[6].style.visibility='hidden';
    layers[8].style.visibility='hidden';
    layers[10].style.visibility='visible';
    for(var a=10;a<anzahl;){ a=a+2;
     layers[a].style.visibility='hidden';
    }
   break;
   }
  case (6):
   {
    layers[0].style.visibility='visible';
    layers[2].style.visibility='hidden';
    layers[4].style.visibility='hidden';
    layers[6].style.visibility='hidden';
    layers[8].style.visibility='hidden';
    layers[10].style.visibility='hidden';
    layers[12].style.visibility='visible';
    for(var a=12;a<anzahl;){ a=a+2;
     layers[a].style.visibility='hidden';
    }
   break;
   }
  case (7):
   {
    layers[0].style.visibility='visible';
    layers[2].style.visibility='hidden';
    layers[4].style.visibility='hidden';
    layers[6].style.visibility='hidden';
    layers[8].style.visibility='hidden';
    layers[10].style.visibility='hidden';
    layers[12].style.visibility='hidden';
    layers[14].style.visibility='visible';
    for(var a=14;a<anzahl;){ a=a+2;
     layers[a].style.visibility='hidden';
    }
   break;
   }
  case (8):
   {
    layers[0].style.visibility='visible';
    layers[2].style.visibility='hidden';
    layers[4].style.visibility='hidden';
    layers[6].style.visibility='hidden';
    layers[8].style.visibility='hidden';
    layers[10].style.visibility='hidden';
    layers[12].style.visibility='hidden';
    layers[14].style.visibility='hidden';
    layers[16].style.visibility='visible';
    break;
   }
  default:
   {
    layers[0].style.visibility='visible';
    layers[2].style.visibility='hidden';
    layers[4].style.visibility='hidden';
    layers[6].style.visibility='hidden';
    layers[8].style.visibility='hidden';
    layers[10].style.visibility='hidden';
    layers[12].style.visibility='hidden';
    layers[16].style.visibility='hidden';
    break;
   }
 }
}