function switchtab(which) {
if (which==1) {
document.getElementById('tab1').style.display="";
document.getElementById('tab2').style.display="none";
document.getElementById('tab3').style.display="none";
document.getElementById('tab4').style.display="none";
document.getElementById('button1').setAttribute("class","home");
document.getElementById('button2').setAttribute("class","menu_in");
document.getElementById('button3').setAttribute("class","menu_in");
document.getElementById('button4').setAttribute("class","menu_in");

} else if (which==2) {
document.getElementById('tab1').style.display="none";
document.getElementById('tab2').style.display="";
document.getElementById('tab3').style.display="none";
document.getElementById('tab4').style.display="none";
document.getElementById('button1').setAttribute("class","home");
document.getElementById('button2').setAttribute("class","menu_act");
document.getElementById('button3').setAttribute("class","menu_in");
document.getElementById('button4').setAttribute("class","menu_in");
}
 else if (which==3) {
document.getElementById('tab1').style.display="none";
document.getElementById('tab2').style.display="none";
document.getElementById('tab3').style.display="";
document.getElementById('tab4').style.display="none";
document.getElementById('button1').setAttribute("class","home");
document.getElementById('button2').setAttribute("class","menu_in");
document.getElementById('button3').setAttribute("class","menu_act");
document.getElementById('button4').setAttribute("class","menu_in");
}
 else {
document.getElementById('tab1').style.display="none";
document.getElementById('tab2').style.display="none";
document.getElementById('tab3').style.display="none";
document.getElementById('tab4').style.display="";
document.getElementById('button1').setAttribute("class","home");
document.getElementById('button2').setAttribute("class","menu_in");
document.getElementById('button3').setAttribute("class","menu_in");
document.getElementById('button4').setAttribute("class","menu_act");
}

}