window.onload=function(){
  document.getElementById("gallery").style.backgroundImage = "url(../img/slideshow/"+real[1]['file']+")";
  var num = document.getElementById("number");
  var margin = Math.round((450-real[1]['height'])/2);
  num.innerHTML = "1";
  num.style.marginTop = margin;}
  
function prev(){
  var num = document.getElementById("number");
  var current = parseInt(num.innerHTML);
  var prev = 1;
  if(current!=1) {prev = current-1;}
  document.getElementById("gallery").style.backgroundImage = "url(../img/slideshow/"+real[prev]['file']+")";
  var num = document.getElementById("number");
  var margin = Math.round((450-real[prev]['height'])/2);
  num.innerHTML = prev;
  num.style.marginTop = margin;}
  
function next(){
  var num = document.getElementById("number");
  var current = parseInt(num.innerHTML);
  var next = 1;
  if(current!=max-1) {next = current+1;}
  document.getElementById("gallery").style.backgroundImage = "url(../img/slideshow/"+real[next]['file']+")";
  var num = document.getElementById("number");
  var margin = Math.round((450-real[next]['height'])/2);
  num.innerHTML = next;
  num.style.marginTop = margin;}