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 Pascal (FPC 2.6.2) (judge verdict: Wrong Answer)

program ec12;
var 
	a,s:array[0..100000] of longint;
	n,m,i,j,ans:longint;
begin 	
	readln(n);
	ans:=0;
	s[0]:=0;
	for i:=1 to n do
	read(a[i]);
	for i:=1 to n do 
	begin 
		s[i]:=s[i-1]+a[i];
		if i>1 then 
		begin 
			if s[i-1]<0 then 
			begin	
				if s[i]<=0 then 
				begin
					if s[i]=0 then 
					begin 
						inc(ans);
						s[i]:=1;
					end
					else
					inc(ans,(-s[i])+1);
				end;
			end
			else
			begin 
				if s[i]>=0 then 
				begin 
					if s[i]=0 then 
					begin 
						inc(ans);
						s[i]:=-1;
					end
					else
					begin 
						inc(ans,s[i]+1);
						s[i]:=-1;
					end;
				end;
			end;
		end
		else
		begin 
			if a[1]=0 then 
			begin 
				if a[2]>0 then 
				begin 	
					inc(ans,a[2]+1);
					s[1]:=-1;
				end
				else
				begin 
					inc(ans,(-a[2])+1);
					s[1]:=1;
				end;
			end;
		end;
	end;
	writeln(ans);
end.