The number of rich customers

# Table: Store
# 
# +-------------+------+
# | Column Name | Type |
# +-------------+------+
# | bill_id     | int  |
# | customer_id | int  |
# | amount      | int  |
# +-------------+------+
# bill_id is the primary key (column with unique values) for this table.
# Each row contains information about the amount of one bill and the customer associated with it.
# 
#  
# 
# Write a solution to report the number of customers who had at least one bill with an amount strictly greater than 500.
# 
# The 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.

import pandas as pd

def count_rich_customers(store: pd.DataFrame) -> pd.DataFrame:
  rich = store[store['amount'] > 500]['customer_id'].nunique()
  return pd.DataFrame({'rich_count': [rich]})