var numImage = 0;

function changeImage(sens, total)
{
  var indexMax = (total-1);
  document.getElementById('image_'+numImage).style.display = 'none';
  numImage += sens;

  if(numImage == total)
  {
    document.getElementById('image_0').style.display = 'block';
    numImage = 0;
  }

  if(numImage == -1)
  {
    document.getElementById('image_'+indexMax).style.display = 'block';
    numImage = indexMax;
  }

  else
    document.getElementById('image_'+numImage).style.display = 'block';

    
  document.getElementById('image_numero').innerHTML = (numImage+1);
 
}