def solution(A):
    max_num = 0
    for i, p in enumerate(A):
        for q in A[i+1:]:
            max_num = max(max_num, q - p)
    return max_num
def solution(A):
    value = 0
    if A == []: return 0
    min_num = A[0]
    
    for num in A[1:]:
        min_num = min(min_num, num)
        value = max(value, num - min_num)
    return value