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 Ruby (2.3.3) (judge verdict: Accepted)

#!/usr/bin/env ruby

STDIN.gets.chomp.to_i
array = STDIN.gets.chomp.split(' ').map(&:to_i)

def get_answer(first, array)
  ans = 0
  sum = first
  array.each do |a|
    if sum * (sum + a) < 0 # sum と (sum + a)の符号が異なる場合
      sum += a
    else
      next_sum = sum < 0 ? 1 : -1
      ans += (next_sum - (sum + a)).abs
      sum = next_sum
    end
  end

  return ans
end

first = array.shift

if first == 0
  ans = [get_answer(1, array), get_answer(-1, array)].min + 1
else
  ans1 = get_answer(first, array)
  ans2 = get_answer((-1 * first/first.abs), array) + first.abs + 1
  ans = [ans1, ans2].min
end

puts ans