add_shortcode('custom_gallery', 'custom_gallery_fn');
    function custom_gallery_fn($attr)
    {
        global $post;
        global $linker_sluger;

        if (isset($attr['orderby'])) {
            $attr['orderby'] = sanitize_sql_orderby($attr['orderby']);
            if (!$attr['orderby'])
                unset($attr['orderby']);
        }

        extract(shortcode_atts(array(
            'order' => 'DESC',
            'orderby' => 'menu_order ID',
            'id' => $post->ID,
            'itemtag' => 'dl',
            'icontag' => 'dt',
            'captiontag' => 'dd',
            'columns' => 3,
            'size' => 'large',
            'ids' => '',
            'exclude' => ''
        ), $attr));

        $id = intval($id);
        if ('RAND' == $order) $orderby = 'none';
        if (!empty($ids)) {
            $ids = preg_replace('/[^0-9,]+/', '', $ids);
            $_attachments = get_posts(array(
                    'include' => $ids,
                    'post_status' => 'inherit',
                    'post_type' => 'attachment',
                    'post_mime_type' => 'image',
                    'order' => 'menu_order ID',
                    'orderby' => 'post__in',
                )
            );

            $attachments = array();
            foreach ($_attachments as $key => $val) {
                $attachments[$val->ID] = $_attachments[$key];
            }
        }

        if (empty($attachments)) return '';

        if (is_page(16)) {

            // Here's your actual output, you may customize it to your need
            $output = '<div class="single-album col-md-12 col-12">';

            // Now you loop through each attachment
            $i = 0;
            foreach ($attachments as $id => $attachment) {


                $i++;
                // Fetch the thumbnail (or full image, it's up to you)
                // $img = wp_get_attachment_image_src($id, 'medium');
                // $img = wp_get_attachment_image_src($id, 'my-custom-image-size');
                $img = wp_get_attachment_image_src($id, 'full');
                //print_r($img);

                $output .= "<div class=\"single-gallery-image\">";
                $output .= "<img src=\"{$img[0]}\" width=\"{$img[1]}\" height=\"{$img[2]}\" alt=\"\" />\n";
                $output .= "</div>";

                if($i==1){
                    break;
                }
            }
            //$output .= "</div>\n";

            $output .= "</div>";

        }
        else {
            // Here's your actual output, you may customize it to your need
            $output = '<div class="gallery-investition-single col-md-12 col-12">
                    <div class="row">';
            // Now you loop through each attachment
            foreach ($attachments as $id => $attachment) {
                // Fetch the thumbnail (or full image, it's up to you)
                // $img = wp_get_attachment_image_src($id, 'medium');
                // $img = wp_get_attachment_image_src($id, 'my-custom-image-size');
                $img = wp_get_attachment_image_src($id, 'full');
                $output .= "<a href=\"{$img[0]}\" class=\"foobox col-md-4 col-12\" rel=\"gallery\">";
                $output .= "<div class=\"single-gallery-image\">";
                $output .= "<img src=\"{$img[0]}\" width=\"{$img[1]}\" height=\"{$img[2]}\" alt=\"\" />\n";
                $output .= "</div>";
                $output .= "</a>";
            }
            //$output .= "</div>\n";
            $output .= "</div>";
            $output .= "</div>";

        }


        return $output;
    }