Add value to hidden form field jquery multiple select options

HTML

<div>
    <form>
        <div id='div_block1'>
            <input type="text" value="" name="a[]" class='input_text flag'>
            <input type="text" value="" name="b[]" class='input_text flag'>
            <input type="text" value="" name="c[]" class='input_text flag'>
            <input type="text" value="" name="a[]" class='input_text flag'>
            <input type="text" value="" name="b[]" class='input_text flag'>
            <input type="text" value="" name="c[]" class='input_text flag'>
            <select id='block1'>
                <option value="" data-value=""></option>
                <option value="1" data-value="11,12,13,6,12,8">1</option>
                <option value="2" data-value="21,22,23,8,10,33">2</option>
                <option value="3" data-value="31,32,33,2,8,6">3</option>
                <option value="4" data-value="41,42,43,22,54,63">4</option>
                <option value="5" data-value="51,52,53,12,34,55">5</option>
            </select>
        </div>
</div>

CSS

div {
    float:left;
    width:100%;
}
input {
    width:50px;
}

JavaScript

$(function () {
    $('select').on('change', function () {
        var div_id = 'div_' + $(this).attr('id');
        var select_val = $(this).find('option:selected').data('value');
        console.log();
        if (select_val != '') {
            var a = select_val.split(',');
            var count = 0;
            $('div#' + div_id + ' .flag').each(function () {
                $(this).val(a[count]);
                ++count;
            });
        } else {
            $('div#' + div_id + ' input.input_text').val('');
        }
    });

});