Hello . Does anyone know how to register for codechef contests ?

For example for the procon 2014 ....

Hello . I have recently seen a question and I want your help ....

We have a sequence of numbers . Each of them is 1 or -1 .

In every second we can choose a contiguous subsequence of them and do

the operation for each of them : a[i] = a[i] * -1

The question is that given the sequence what is the minimum time needed to transform all of the numbers to 1 ?

Example

Input :

6

1 -1 -1 1 -1 1

Output :

2