<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<!------ Include the above in your HEAD tag ---------->
<!DOCTYPE html>
<html>
<body>
<input type="number" id="txt">
<button onclick="add()">add</button>
<p id="demo"></p>
<script>
function add(){
var tx=document.getElementById('txt').value
var lk=""
for (var i=tx;i>=0;i--){
if(i%2==0){
lk+=i+"<br>"
}
}
document.getElementById('demo').innerHTML=lk
}
</script>
</body>
</html>
