function calculate() {
	var r = document.getElementById("r").value;
	var h = document.getElementById("h").value;
	var volume;
	if (r != "" && h != "") {
		r = parseFloat(r);
		h = parseFloat(h);
		volume = ((Math.PI*r*r*h)/3);
		document.getElementById("volume").innerHTML = "volume: " + volume;
	}
}