// JavaScript Document
prev="s1";
prevNum=1;
prevCon ="content1";

function chgBtn(btn,num,namePic){
if(prev!=btn){
document.getElementById("mainpic").setAttribute("src","images/"+namePic+num+".jpg");

document.getElementById(prevCon).style.display="none";
document.getElementById("content"+num).style.display="block";

document.getElementById(prev).style.backgroundPosition="top";
document.getElementById(btn).style.backgroundPosition="bottom";
}else{
}
prevNum = num;
prevCon = "content"+num;
prev=btn;
}