Fibonacci Series using JavaScript

/*fibonacci series*/
<html>
<head>
</head>
<body>
<script>
var a=0, b=1, c, i;
var num=parseInt(prompt("Enter for limit"));
for (i=1;i<=num;i++)
{
document.write("<br>" + a);
c=a+b;
a=b;
b=c;
}
</script>
</body>
</html>