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<script type="text/javascript">
$(document).ready(function(){
$(".reg_form div input").animate({opacity:'0.4'},0)
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<form action="reg.php" method="post" class="reg_form">
<div class="inp"><input type="text" name="name" value="Ваше имя" /></div>
<div class="inp"><input type="text" name="fname" value="Ваша фамилия" /></div>
<div class="inp"><input type="text" name="mail" value="Ваш маил" /></div>
<div class="inp"><input type="password" name="pass" value="Ваш пароль" /></div>
</form>