function checkForm() {
    var w = document.input_data;
    if (!f.who.value || !f.what.value ||
        f.start_year.value < 2010 || f.start_month.value < 1 || f.start_day.value < 1 || f.duration.value < 1 ||
        f.where.value === 'other' && !f.where_o.value ) {
        alert('Please make sure that all fields are filled in with proper values.');
        return false;
    }

    return true;
}