Problem:
Score : 300 points

Problem Statement

You are given an integer sequence of length N. The i-th term in the sequence is a_i.
In one operation, you can select a term and either increment or decrement it by one.

At least how many operations are necessary to satisfy the following conditions?

For every i (1≤i≤n), the sum of the terms from the 1-st through i-th term is not zero.

For every i (1≤i≤n-1), the sign of the sum of the terms from the 1-st through i-th term, is different from the sign of the sum of the terms from the 1-st through (i+1)-th term.

Constraints

2 ≤ n ≤ 10^5

|a_i| ≤ 10^9

Each a_i is an integer.

Input

Input is given from Standard Input in the following format:

n
a_1 a_2 ... a_n

Output

Print the minimum necessary count of operations.

Sample Input 1

4
1 -3 1 0

Sample Output 1

4

For example, the given sequence can be transformed into 1, -2, 2, -2 by four operations. The sums of the first one, two, three and four terms are 1, -1, 1 and -1, respectively, which satisfy the conditions.

Sample Input 2

5
3 -6 4 -5 7

Sample Output 2

0

The given sequence already satisfies the conditions.

Sample Input 3

6
-1 4 3 2 -5 4

Sample Output 3

8

Solution in Rust (1.42.0) (judge verdict: Accepted)

use proconio::input;

fn main() {
    input! {
        n: usize,
        a: [i64; n],
    };

    let a_e = {
        let mut res = 0_i64;
        let mut sum = 0_i64;
        for (i, &a_i) in a.iter().enumerate() {
            sum += a_i;
            if i % 2 == 0 {
                if sum > 0 {
                    // do nothing
                } else {
                    res += 1 - sum;
                    sum = 1;
                }
            } else {
                if sum >= 0 {
                    res += 1 + sum;
                    sum = -1;
                } else {
                    // do nothing
                }
            }
        }
        res
    };

    let a_o = {
        let mut res = 0_i64;
        let mut sum = 0_i64;
        for (i, &a_i) in a.iter().enumerate() {
            sum += a_i;
            if i % 2 == 0 {
                if sum >= 0 {
                    res += 1 + sum;
                    sum = -1;
                } else {
                    // do nothing
                }
            } else {
                if sum > 0 {
                    // do nothing
                } else {
                    res += 1 - sum;
                    sum = 1;
                }
            }
        }
        res
    };

    let ans = std::cmp::min(a_e, a_o);
    println!("{}", ans);
}