function daysOfFebruary(year) {
  // Calculate leap years
  a = year % 4;
  b = year % 100;
  c = year % 400;
  if (a == 0) {
    if (b == 0) {
      if (c == 0) {
        return 28;
      } else {
        return 29;
      }
    } else {
      return 29;
    }
  } else {
    return 28;
  }
}
function calcCarnival(form,divid)
{
  year = parseInt(form.year.value);
  if (year != 0)
  {
    a = year % 19;
    b = year % 4;
    c = year % 7;
    M= 24; N = 5;
    d = (19 * a + M) % 30;
    e = (2 * b + 4 * c + 6 * d + N) % 7;
    if ((22 + d + e) <= 31)
      { eastDateMonth = 3;
        eastDateDay = 22 + d + e; }
    else
      { eastDateMonth = 4;
        eastDateDay = d + e - 9; }
    todo = 47;
    endDateMonth = eastDateMonth;
    endDateDay = 1; todo = todo - (eastDateDay - 1);
    if (endDateMonth == 4) {
      if (todo > 31) {
        endDateDay = (32 + daysOfFebruary(year)) - todo;
        endDateMonth = endDateMonth - 2;
      } else {
        endDateDay = 32 - todo;
        endDateMonth = endDateMonth - 1;
      }
    } else {
      endDateDay = (daysOfFebruary(year) + 1) - todo;
      endDateMonth = endDateMonth - 1;
    }
    beginDateMonth = endDateMonth;
    beginDateDay = endDateDay - 4;
    if (beginDateDay < 1) {
      beginDateMonth = beginDateMonth - 1;
      beginDateDay = daysOfFebruary(year) - beginDateDay;
    }
    strBegDate = beginDateDay + '-' + beginDateMonth + '-' + year;
    strEndDate = endDateDay + '-' + endDateMonth + '-' + year;
    myDiv = document.getElementById(divid);
    myDiv.innerHTML = '<i>vrijdag ' + strBegDate + '<br>tot en met<br>dinsdag ' + strEndDate+'</i><br><br>';
  }
  else
  {
    myDiv.innerHTML = '';
  }

}