var amenitiesCount = 0;

function countAmenities(object) {
    if (object.checked) {
        amenitiesCount++;
        disableUncheckedBoxes(true);
    } else {
        amenitiesCount--;
        disableUncheckedBoxes(false);
    }
}

function controlUncheckedBox(id, isDisabled) {
    if (!document.getElementById(id).checked) {
        document.getElementById(id).disabled = isDisabled;
    }
}

function disableUncheckedBoxes(isDisabled) {
    if (amenitiesCount == 3 || !isDisabled) {
        controlUncheckedBox("am1", isDisabled);
        controlUncheckedBox("am2", isDisabled);
        controlUncheckedBox("am3", isDisabled);
        controlUncheckedBox("am4", isDisabled);
        controlUncheckedBox("am5", isDisabled);
        controlUncheckedBox("am6", isDisabled);
        controlUncheckedBox("am7", isDisabled);
        controlUncheckedBox("am8", isDisabled);
        controlUncheckedBox("am9", isDisabled);
    }
}

function updateAmenitiesCount() {
    if (document.getElementById("am1").checked) {amenitiesCount++;}
    if (document.getElementById("am2").checked) {amenitiesCount++;}
    if (document.getElementById("am3").checked) {amenitiesCount++;}
    if (document.getElementById("am4").checked) {amenitiesCount++;}
    if (document.getElementById("am5").checked) {amenitiesCount++;}
    if (document.getElementById("am6").checked) {amenitiesCount++;}
    if (document.getElementById("am7").checked) {amenitiesCount++;}
    if (document.getElementById("am8").checked) {amenitiesCount++;}
    if (document.getElementById("am9").checked) {amenitiesCount++;}
}