Problem:
Score : 400 points

Problem Statement

There are N integers, A_1, A_2, ..., A_N, arranged in a row in this order.

You can perform the following operation on this integer sequence any number of times:

Operation: Choose an integer i satisfying 1 \leq i \leq N-1. Multiply both A_i and A_{i+1} by -1.

Let B_1, B_2, ..., B_N be the integer sequence after your operations.

Find the maximum possible value of B_1 + B_2 + ... + B_N.

Constraints

All values in input are integers.

2 \leq N \leq 10^5

-10^9 \leq A_i \leq 10^9

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the maximum possible value of B_1 + B_2 + ... + B_N.

Sample Input 1

3
-10 5 -4

Sample Output 1

19

If we perform the operation as follows:

Choose 1 as i, which changes the sequence to 10, -5, -4.

Choose 2 as i, which changes the sequence to 10, 5, 4.

we have B_1 = 10, B_2 = 5, B_3 = 4. The sum here, B_1 + B_2 + B_3 = 10 + 5 + 4 = 19, is the maximum possible result.

Sample Input 2

5
10 -4 -8 -11 3

Sample Output 2

30

Sample Input 3

11
-1000000000 1000000000 -1000000000 1000000000 -1000000000 0 1000000000 -1000000000 1000000000 -1000000000 1000000000

Sample Output 3

10000000000

The output may not fit into a 32-bit integer type.

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io::stdin;
use std::str::FromStr;
use std::cmp::min;

fn main(){
    let n: usize = get_one();
    let xs: Vec<i64> = get_vec();
    let can_all_positive = {
        let mut n_neg = 0;
        for &x in &xs {
            if x == 0 { n_neg=0; break; };
            if x < 0 { n_neg += 1 };
        }
        n_neg % 2 == 0
    };
    let abss: Vec<i64> = xs.iter().map(|&x|x).map(i64::abs).collect();
    let m = vec_min(&abss);
    let mut ans = vec_sum(&abss);
    if !can_all_positive {
        ans -= m * 2;
    }
    println!("{}", ans);
}

#[allow(dead_code)]
fn get_line() -> String {
    let mut s = String::new();
    match stdin().read_line(&mut s){
        Ok(_) => {s.trim().to_string()}
        Err(_) => String::new()
    }
}

#[allow(dead_code)]
fn get_vec<T: std::str::FromStr>() -> Vec<T> {
    let line = get_line();
    line.split_whitespace().filter_map(|x| x.parse().ok()).collect()
}

#[allow(dead_code)]
fn get_one<T: FromStr + Copy>() -> T {
    let v = get_vec();
    v[0]
}

#[allow(dead_code)]
fn get_pair<T: FromStr + Copy>() -> (T, T) {
    let v = get_vec();
    (v[0], v[1])
}

#[allow(dead_code)]
fn get_triple<T: FromStr + Copy>() -> (T, T, T) {
    let v = get_vec();
    (v[0], v[1], v[2])
}

#[allow(dead_code)]
fn get_chars() -> Vec<char> {
    get_line().chars().collect()
}

#[allow(dead_code)]
fn vec_min(xs: &Vec<i64>) -> i64 {
    xs.iter().map(|&x|x).fold(std::i64::MAX, std::cmp::min)
}

#[allow(dead_code)]
fn vec_max(xs: &Vec<i64>) -> i64 {
    xs.iter().map(|&x|x).fold(std::i64::MIN, std::cmp::max)
}

#[allow(dead_code)]
fn vec_sum(xs: &Vec<i64>) -> i64 {
    xs.iter().fold(0, |acc, &x| acc+x)
}