function next_pic(e) 
 {
  var i = document.getElementById(e).src;
      begin = i.lastIndexOf("/")+1;
      len = i.lastIndexOf(".");
      num = i.substring(begin,len);
   if (e=='0') {if (num<7) {num++;} else {num=0;}}  
   if (e=='1') {if (num<12) {num++;} else {num=8;}}
   if (e=='2') {if (num<21) {num++;} else {num=14;}}
   if (e=='3') {if (num<23) {num++;} else {num=22;}}
   document.getElementById(e).src = 'images/villa/'+num+'.jpg';
 }