<head></head>
<body>
<script>
const floors = 9;
const flats = 4;
let flatNum = +prompt("Enter flat number");
let entrance = Math.floor(flatNum / flats / floors);
let floor = Math.floor((flatNum - (entrance * 36)) / flats);
alert("Entrance: " + (entrance + 1) + ", Floor: " + (floor+1));
</script>
</body>