currentPage = 0;

function changePage (pageNum)
{
  currentPageId = "page-" + currentPage;
  newPageId = "page-" + pageNum;
  
  currentPage = document.getElementById (currentPageId);
  newPage = document.getElementById (newPageId);

  currentPage.style.display = "none";
  newPage.style.display = "block";

  currentPage = pageNum;
}

function nextPage ()
{
  changePage(currentPage + 1);
}

function previousPage ()
{
  changePage(currentPage - 1);
}