<!doctype html>
<html>
<head>
<script>
var i=0, n, sum=0, temp;
function fun()
{
n = parseInt(document.getElementById("n").value);
if(n)
{
document.getElementById("nVal").innerHTML = n;
document.getElementById("tme").innerHTML = i+1;
i++;
temp = document.getElementById("one");
temp.style.display = "none";
temp = document.getElementById("two");
temp.style.display = "block";
}
}
function add()
{
if(i==n)
{
temp = document.getElementById("two");
temp.style.display = "none";
temp = document.getElementById("three");
temp.style.display = "block";
}
num = parseInt(document.getElementById("num").value);
if(num)
{
sum = sum + num;
document.getElementById("num").value = null;
document.getElementById("tme").innerHTML = i+1;
i++;
}
}
function res()
{
document.getElementById("result").value = sum;
}
</script>
</head>
<body>
<p id="one">Enter the Value of n: <input id="n">
<button onclick="fun()">ENTER</button></p>
<p id="two" style="display:none;">Enter <span id="nVal"></span>
Numbers. Input No. <span id="tme"></span>:
<input id="num"><button id="btn" onclick="add()">ENTER</button></p>
<p id="three" style="display:none;"><button onclick="res()">Add</button>
<input id="result"></p>
</body>
</html>