# This problem was asked by Facebook.
#
# Given a array of numbers representing the stock prices of a company in chronological order,
# write a function that calculates the maximum profit you could have made from buying and selling that stock once.
# You must buy before you can sell it.
#
# For example, given [9, 11, 8, 5, 7, 10], you should return 5,
# since you could buy the stock at 5 dollars and sell it at 10 dollars.
import sys

def solve(list):
    if not list or len(list) < 2:
        return

    diff = -sys.maxsize
    min = list[0]
    for a in list:
        if a - min > diff:
            diff = a - min
        if a < min:
            min = a
    return diff

# print("Enter the prices: ")
# l = list(map(int, input().split))
print(solve([9, 11, 8, 5, 7, 10]))