function ovulation_date() {

// Get input values
	var y = parseInt(document.getElementById('year').value, 10);
	var m = parseInt(document.getElementById('month').value, 10);
	var d = parseInt(document.getElementById('day').value, 10);
	var c = parseInt(document.getElementById('olength').value, 10); // cycle

// Get the start of the ovulation
    var starto = new Date(y, m-1, d);
	var daymsecs = 60*60*24*1000;
	starto.setTime(starto.getTime() + ((c * daymsecs) - daymsecs*14));

	y = starto.getFullYear();
	m = starto.getMonth()+1;
	d = starto.getDate();

// Report the result
	document.getElementById('result').innerHTML = "" + y + ". " + (m < 10 ? "0"+m : m) + ". " + (d < 10 ? "0"+d : d) + ".";

	starto.setTime(starto.getTime() - daymsecs*3);
	y = starto.getFullYear();
	m = starto.getMonth()+1;
	d = starto.getDate();
	var fertilespan = "" + y + ". " + (m < 10 ? "0"+m : m) + ". " + (d < 10 ? "0"+d : d) + ". - ";
	starto.setTime(starto.getTime() + daymsecs*5);
	y = starto.getFullYear();
	m = starto.getMonth()+1;
	d = starto.getDate();
	fertilespan += "" + y + ". " + (m < 10 ? "0"+m : m) + ". " + (d < 10 ? "0"+d : d) + ".";

	document.getElementById('fertile').innerHTML = fertilespan;

}