# -*- coding: utf-8 -*-
number = int(input())
arr = [int(i) for i in input().split()]
arr1 = []
i = 0
j = 1
flag = True
while i < len(arr):
    if arr[i] < 0:
        flag = False
    if j % 2 == 0:
        arr1.append(-arr[i])
    else:
        arr1.append(arr[i])
    i += 1
    j += 1
if flag:
    best1 = arr1[0]
    summ = 0
    for i in arr1:
        summ = max(i, i + summ)
        best1 = max(best1, summ)
    print(best1)
else:
    arr2 = []
    i = 1
    j = 1
    while i < len(arr):
        if j % 2 == 0:
            arr2.append(-arr[i])
        else:
            arr2.append(arr[i])
        i += 1
        j += 1
    best1 = 0
    best2 = 0
    for i in arr1:
        best1 += i
    for i in arr2:
        best2 += i
    if best1 > best2:
        print(best1)
    elif 0 > best1 and 0 > best2:
        print(0)
    else:
        print(best2)