#include<bits/stdc++.h>
using namespace std;



int main()
{
    int n,arr[20000],i,j,k,steps=0,a,b,c,d,e,mn,pos;
    while(cin>>n)
    {
        steps=0,mn=1e9,pos=0;
        for(i=0; i<n; i++)
            cin>>arr[i];
        while(1)
        {
            pos=-1;
            mn=1e9;
            for(i=0; i<n; i++)
            {
                if(arr[i]<mn && arr[i]<0)
                {
                    mn=arr[i];
                    pos=i;
                }
            }
            if(pos==-1)
            {
                break;
            }
            arr[pos]*=(-1);
         //   cout<<"arr[pos] "<<arr[pos]<<endl;
            if(pos==n-1)
            {
                arr[n-2]-=arr[pos];
                arr[0]-=arr[pos];
            }
            else if(pos==0)
            {
                arr[n-1]-=arr[pos];
                arr[1]-=arr[pos];
            }
            else
            {
                arr[pos-1]-=arr[pos];
                arr[pos+1]-=arr[pos];
            }
            steps++;
        }
        cout<<steps<<endl;
    }
    return 0;
}