来源：https://codeforces.com/contest/33/problem/C
Wonderful Randomized Sum
Learn, learn and learn again — Valera has to do this every day. He is studying at mathematical school, where math is the main discipline. The mathematics teacher loves her discipline very much and tries to cultivate this love in children. That's why she always gives her students large and difficult homework. Despite that Valera is one of the best students, he failed to manage with the new homework. That's why he asks for your help. He has the following task. A sequence of n numbers is given. A prefix of a sequence is the part of the sequence (possibly empty), taken from the start of the sequence. A suffix of a sequence is the part of the sequence (possibly empty), taken from the end of the sequence. It is allowed to sequentially make two operations with the sequence. The first operation is to take some prefix of the sequence and multiply all numbers in this prefix by ?-?1. The second operation is to take some suffix and multiply all numbers in it by ?-?1. The chosen prefix and suffix may intersect. What is the maximum total sum of the sequence that can be obtained by applying the described operations?
Input
The first line contains integer n (1?≤?n?≤?105) — amount of elements in the sequence. The second line contains n integers ai (?-?104?≤?ai?≤?104) — the sequence itself.
Output
The first and the only line of the output should contain the answer to the problem.
Examples
input
Copy
3 -1 -2 -3
output
Copy
6
input
Copy
5 -4 2 0 5 0
output
Copy
11
input
Copy
5 -1 10 -5 10 -2
output
Copy
18f
翻译：
?学习，再学习——瓦莱拉每天都要这样做。他正在数学学校学习，数学是主要学科。数学老师非常喜欢她的学科，并试图在孩子们身上培养这种爱。这就是为什么她总是给她的学生大量而困难的家庭作业。尽管瓦莱拉是最好的学生之一，但他未能完成新的家庭作业。这就是为什么他请求你的帮助。他有以下任务。给出了 ??n?? 个数字的序列。序列的前缀是从序列开头取出的序列的一部分（可能为空）。序列的后缀是从序列末尾取出的序列部分（可能为空）。允许对序列按顺序进行两次操作。第一个操作是采用序列的某个前缀，并将此前缀中的所有数字乘以 ?? -1??。第二个操作是取一些后缀，并将其中的所有数字乘以??-1??。所选的前缀和后缀可能会相交。通过应用所述操作可以获得的序列的最大总和是多少？?
?第一行包含整数 ??n? (1?≤?n?≤?105?） ― 序列中元素的数量。第二行包含 ??n?? 个整数??一个??我? (?- 10?4?≤ ??a??i?≤ 10?4?） — 序列本身。?
?输出的第一行和唯一行应包含问题的答案。?