# you can write to stdout for debugging purposes, e.g.
# print("this is a debug message")

def solution(A):
    # write your code in Python 3.6
    if A == []:
        return 0
    cost = [0] * (len(A)-1)
    for i in range(len(A)-1):
        cost[i] = A[i+1] - A[i]
    s = 0
    maxS = 0
    for c in cost:
        if s > 0:
            s += c
        else:
            s = c
        if s > maxS:
            maxS = s
    return max(maxS, 0)