# -*- coding: utf-8 -*-
number = int(input())
arr = [int(i) for i in input().split()]
amountOfElement = len(arr)
best = 0
i = 0
while i < amountOfElement:
    summ = 0
    j = i
    counter = 1
    while j < amountOfElement:
        if counter % 2 == 0:
            summ += -arr[j]
        else:
            summ += arr[j]
        j += 1
        counter += 1
    best = max(summ, best)
    i += 1
print(best)