function rewrite_days()
{
    var days = document.getElementById("day");
    var month = document.getElementById("month");
    var year = document.getElementById("year");
    var days_in_month = new Array(31,28,31,30,31,30,31,31,30,31,30,31);
    if (month.value != 0)
    {
        if ((year.value % 4 == 0) && (month.value == 2))
        {
            days.length = 10;
            days.item(29).value = 29;
            days.item(29).text = 29;
        }
        else
        {
            
            days.length = days_in_month[month.value - 1] + 1;
 
            for (var i = 29; i < days.length; i++)
            {
                days.item(i).value = i;
                days.item(i).text = i;
            }
        }
    }
}