$(document).ready(function(){
    lastBlock = $("#a1");
    maxWidth = 650;
    minWidth = 35;	

    $(".slider").hover(
      function(){
        $(lastBlock).animate({width: minWidth+"px"}, { queue:false, duration:700  });
        $(this).animate({width: maxWidth+"px"}, { queue:false, duration:700});
        lastBlock = this;
      });
});