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: Wrong Answer)

n = int(input())
a = list(map(int,input().split()))
A = a[:]
count_plus=0
count_minus=0
x = 0
y = 0
for i in range(n):
  if i%2==0:
    x+=a[i]
    if x<0:
      count_plus+=-1*x+1
      a[i]+=-1*x+1
      x+=-1*x+1
  else:
    x+=a[i]
    if x>0:
      count_plus+=x+1
      a[i]+=-1*x-1
      x+=-1*x-1   
for i in range(n):
  if i%2==0:
    y+=A[i]
    if y>0:
      count_minus+=y+1
      A[i]+=-1*y-1
      y+=-1*y-1
  else:
    y+=A[i]
    if y<0:
      count_minus+=-1*y+1
      A[i]+=-1*y+1
      y+=-1*y+1
if x==0:
  count_plus+=1
if y==0:
  count_minus+=1
print(min(count_plus,count_minus))