Best Time to Buy and Sell Stock

prices[i] is a stock's price on day i. You may buy once and sell once, and the sale must be on a later day than the purchase.

Return the largest profit you can make. If every trade would lose money, return 0 (just don't trade).

Example 1

Input: prices = [7,1,5,3,6,4]
Output: 5
Buy at 1 (day 1), sell at 6 (day 4).

Example 2

Input: prices = [7,6,4,3,1]
Output: 0
The price only falls.

Example 3

Input: prices = [2,4,1]
Output: 2
Selling before buying isn't allowed.

Constraints

• 1 ≤ len(prices) ≤ 10^5
• 0 ≤ prices[i] ≤ 10^5