Write an SQL query to report the number of customers who had at least one bill with an amount strictly greater than 500.
The query result format is in the following example.

Example 1:
Input: Store table:

+---------+-------------+--------+

| bill_id | customer_id | amount |

+---------+-------------+--------+

| 6 ? ? ? | 1 ? ? ? ? ? | 549 ? ?|

| 8 ? ? ? | 1 ? ? ? ? ? | 834 ? ?|

| 4 ? ? ? | 2 ? ? ? ? ? | 394 ? ?|

| 11 ? ? ?| 3 ? ? ? ? ? | 657 ? ?|

| 13 ? ? ?| 3 ? ? ? ? ? | 257 ? ?|

+---------+-------------+--------+

Output:

+------------+

| rich_count?|

+------------+

| 2 ? ? ? ? ?|

+------------+

Explanation: Customer 1 has two bills with amounts strictly greater than 500.Customer 2 does not have any bills with an amount strictly greater than 500.Customer 3 has one bill with an amount strictly greater than 500.