Bulb

#include<stdio.h>
#include<queue>
using namespace std;

struct elem{
    int state;
    int dis;
    bool operator < (const elem& rhs)const
    {
        return dis > rhs.dis;
    }
};

int main()
{
    int n;
    scanf("%d",&n);
    if(n == 1){
        int x;
        scanf("%d",&x);
        printf("%d",x);
        return 0;
    }

    int state = 0;
    for(int i = n - 1 ; i >= 0 ; i --){
        int x;
        scanf("%d",&x);
        state += (1<<i)*x;
    }
    bool visited[(1<<n)];
    int dist[(1<<n)];

    for(int i = 0 ; i < (1<<n) ; i ++){
        visited[i] = false;
        dist[i] = 1e9;
    }
    dist[state] = 0;


    int ans = -1;
    queue<int> q;
    q.push(state);
    while(!q.empty()){
        int u = q.front();//.state;
        q.pop();
        if(u == 0){
            break;
        }
        for(int i = 0 ; i < n ; i ++){
            int xp;
            if(i == 0){
                xp = u xor (1<<0);
                xp = xp xor (1<<1);
            }
            else if(i == n - 1){
                xp = u xor (1<<n-1);
                xp = xp xor (1<<n-2);
            }
            else{
                xp = u xor (1<<i);
                xp = xp xor (1<<(i+1));
                xp = xp xor (1<<(i-1));
            }
            if(!visited[xp] && dist[u] + 1 < dist[xp]){
                dist[xp] = dist[u] + 1;
                q.push(xp);
            }
        }
    }
    printf("%d",(dist[0] == 1e9 ? -1 : dist[0]));
    return 0;
}