# You are given an integer array of prices where prices[i] is the price of a given stock on the ith day.
# On each day, you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However, you can buy it then immediately sell it on the same day.
# Find and return the maximum profit you can achieve.
# Input: prices = [7,1,5,3,6,4]
# Output: 7
# Input: prices = [1,2,3,4,5]
# Output: 4
# Input: prices = [7,6,4,3,1]
# Output: 0
