Implement automatic scrolling using jQuery

HTML

<br/>
<strong>Time (in Seconds) :</strong> <input type="text" id="txtTime" value="3" />
&nbsp;&nbsp;<strong>Pixel :</strong> <input type="text" id="txtPixel" Value="100"/>
<input type="button" class="button" id="btnStart" value="Start Scrolling" />
<input type="button" class="button" id="btnStartHidden" style="display:none;" value="Start Scrolling" />
<input type="button" class="button" id="btnStop" value="Stop Scrolling" />
<br/><br/><br/>
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        elit eleifend consectetur ut eu velit. Suspendisse laoreet malesuada nulla tristique
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        sapien eget egestas. Mauris erat neque, iaculis a molestie non, feugiat quis tortor.
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       ...

CSS

body {
  font-family: calibri;
}
input[type="text"] {
	width:50px;
}
#btnStop {
	 position: absolute;
	 right:0px;
	 top: 0px;
	 background-color: red;
	 font-family: calibri;
}

#btnStartHidden {
	position: absolute;
	left:0px;
	top: 0px;
}

.button {
	background-color: #4CAF50; /* Green */
	border: none;
	color: white;
	padding: 10px 12px;
	text-align: center;
	text-decoration: none;
	display: inline-block;
	font-size: 16px;
	font-family: calibri;
}

JavaScript

$(document).ready(function () {
	var scrollInterval = false;
	var iSeconds = $('#txtTime').val();
	iSeconds = parseInt(iSeconds) * 1000;

	function AutomaticScroll() {
		var nScrollTop = $(window).scrollTop();
		if (parseInt(nScrollTop + $(window).height()) == $(document).height()) {
			clearInterval(scrollInterval);
			return;
		}
		var nPixel = $('#txtPixel').val();
		nScrollTop = nScrollTop + parseInt(nPixel);
		$('html, body').animate({ scrollTop: nScrollTop }, 1000);
		$('#btnStop').animate({"top": nScrollTop + "px"}, 1500);
	}
	$(window).scroll(function(){
		var nScrollTop = $(window).scrollTop();
		if(parseInt(nScrollTop) == 0)
		{
			$('#btnStartHidden').hide();
			$('#btnStop').animate({"top": nScrollTop + "px"}, 1500);
		}
	});

	$('#btnStart').click(function() {
		scrollInterval = setInterval(AutomaticScroll, iSeconds);
	});

	$('#btnStartHidden').click(function() {
		scrollInterval = setInterval(AutomaticScroll, iSeconds);
		$(this).hide(1000);
	});

	$('#btnStop').click(function() {
		clearInterval(scrollInterval);
		var nScrollTop = $(window).scrollTop();
		if(nScrollTop != 0)
		{
			$('#btnStartHidden').show(500);
			$('#btnStartHidden').animate({"top": nScrollTop + "px"}, 500);
		}
	});
});