Prefix in woocommerce order number

functions.php

add_filter( 'woocommerce_order_number', 'wpdesk_woocommerce_order_number_prefix_suffix', 20 );
function wpdesk_woocommerce_order_number_prefix_suffix( $order_id ) {
    $prefix = 'X/';
    $suffix = '/Y';
    $new_order_id = $prefix . $order_id . $suffix;
    return $new_order_id;
}