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 Python (3.4.3) (judge verdict: Accepted)

n = int(input())
l = list(map(int, input().split()))
even = 0
e_sum = 0
odd = 0
o_sum = 0
for i in range(n):
  e_sum += l[i]
  if i % 2 == 0 and e_sum <= 0:
    even += abs(e_sum)+1
    e_sum = 1
  elif not i % 2 == 0 and e_sum >= 0:
    even += abs(e_sum)+1
    e_sum = -1

for i in range(n):
  o_sum += l[i]
  if i % 2 == 0 and o_sum >= 0:
    odd += abs(o_sum)+1
    o_sum = -1
  elif not i % 2 == 0 and o_sum <= 0:
    odd += abs(o_sum)+1
    o_sum = 1

print(min(even, odd))