function select_area(area) {
  var allTags=document.getElementsByTagName("div");
  for (i=0; i<allTags.length; i++) {
    if (allTags[i].className=="cont_area") {
      allTags[i].style.display="none";
    }
  }
  document.getElementById('cont_'+area).style.display = 'block';
}