function changetab(num){
var num;
var idn;
var cn;
var sh;
document.getElementById('n1').className='n1';
document.getElementById('n2').className='n2';
document.getElementById('n3').className='n3';
document.getElementById('n4').className='n4';
document.getElementById('s1').style.display='none';
document.getElementById('s2').style.display='none';
document.getElementById('s3').style.display='none';
document.getElementById('s4').style.display='none';
idn='n' + num;
sh='s' + num;
cn=idn + num;
document.getElementById(idn).className=cn;
document.getElementById(sh).style.display='block';
}