#描述#
Bob is an ACMer of ZJUT, he wanted to increase his energy by eating AC-APPLEs.

There are N(1 <= N <= 150,000) AC-APPLEs, each AC-APPLE had a magic value "v" which is a positive integer and not bigger than 500.

Bob visited AC-APPLEs which are given in order, every time he faced an AC-APPLE, he can choose "eat this one" or "pass this one". The odd time Bob ate, he increases v units energy. The even time Bob ate, he decreases v units energy.

Before eating any AC-APPLE, Bob's energy is 0.

Please calculate the Maximum Energy Bob can increase by eating AC-APPLEs.

#格式#
##输入格式##
The input will consist of more than one data set.

Each data set has two lines.
First line has an integer N.
Second line has N integers which means the magic value of each AC-APPLEs.

##输出格式##
the Maximum Energy Bob can increase

#样例1#
##样例输入1##

8
7 2 1 8 4 3 5 6

##样例输出1##

17

#限制#
1000ms
32768KB

#提示#

#来源#
BobKing