$( window ).scroll(function(){
    var scrollHeight = $( window ).scrollTop();
	var section0 = $('.mt-logo').outerHeight();
	//var section1 = $('.main-box').outerHeight() + $('.nav-top').outerHeight();
    if( scrollHeight > section0 ){
        $( '.mt-pc-fl' ).addClass('on');
        $( '.mt-pc-fl2' ).addClass('on');
    }else{
        $( '.mt-pc-fl' ).removeClass('on');
        $( '.mt-pc-fl2' ).removeClass('on');
    }
});