function alertSize() {
  var myWidth = 0, myHeight = 0;
  if( typeof( window.innerWidth ) == 'number' ) {
    //Non-IE
    $myHeight = window.innerHeight;
  } else if( document.documentElement && ( document.documentElement.clientWidth || document.documentElement.clientHeight ) ) {
    //IE 6+ in 'standards compliant mode'
    $myHeight = document.documentElement.clientHeight;
  } else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
    //IE 4 compatible
    $myHeight = document.body.clientHeight;
  }

    $mainh=document.getElementById('main').offsetHeight;

    if ($mainh < $myHeight) {
        $footer=document.getElementById('footer').offsetHeight;
        $newheight=$myHeight-$footer;
        document.getElementById('leftmain').style.height=$newheight+'px';
    }

}


alertSize();