You are given an array of stock prices where $\textrm{prices}[i]$ is the price of a given stock on the $\textrm{ith}$ day.

You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.

Write a python program that will return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.

Example 1:

Input: prices = [7,1,5,3,6,4]
Output: 5
# Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
# Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.

Example 2:

Input: prices = [7,6,4,3,1]
Output: 0
# Explanation: In this case, no transactions are done and the max profit = 0.

Fill in the function below to complete your program:

from typing import List

def buy_and_sell_stock(prices: List[int]) -> int:
   """Write your code here"""
   return None