addsubtract
Problem Statement
Joisino has a formula consisting of N terms: A1 op1 A2 ... opN-1 AN.
Here, Ai is an integer, and opi is an binary operator either + or -.
Because Joisino loves large numbers, she wants to maximize the evaluated value of the formula by inserting an arbitrary number of pairs of parentheses (possibly zero) into the formula.
Opening parentheses can only be inserted immediately before an integer, and closing parentheses can only be inserted immediately after an integer.
It is allowed to insert any number of parentheses at a position.
Your task is to write a program to find the maximum possible evaluated value of the formula after inserting an arbitrary number of pairs of parentheses.
Constraints
- 1≦N≦105
- 1≦Ai≦109
- opi is either
+ or -.
Input
The input is given from Standard Input in the following format:
N
A1 op1 A2 ... opN-1 AN
Output
Print the maximum possible evaluated value of the formula after inserting an arbitrary number of pairs of parentheses.
Sample Input 1
3
5 - 1 - 3
Sample Output 1
7
The maximum possible value is: 5 - (1 - 3) = 7.
Sample Input 2
5
1 - 2 + 3 - 4 + 5
Sample Output 2
5
The maximum possible value is: 1 - (2 + 3 - 4) + 5 = 5.
Sample Input 3
5
1 - 20 - 13 + 14 - 5
Sample Output 3
13
The maximum possible value is: 1 - (20 - (13 + 14) - 5) = 13.