#include <bits/stdc++.h>
using namespace std;
const int maxn=1e5+10;
int a[maxn],dp[maxn],n;
int work(int x,int id){
    if(a[id]==0)x=0;
    else if(a[id]==1)x=15;
    else if(a[id]==2)x=15;
    else if(a[id]==3)x--;
    else if(a[id]==4)x--;
    else if(a[id]==5);
    else if(a[id]==6)x++;
    else if(a[id]==7)x+=3;
    return x;
}
int dfs(int x,int id,int step){
    if(id>n||id<1)return step;
    x=work(x,id);
    if(x==0)return step;
    return max(dfs(x,id<<1,step+1),dfs(x,id<<1|1,step+1));
}
signed main() 
{

    freopen("traversal.in","r",stdin);
    freopen("traversal.out","w",stdout);
    cin>>n;
    for(int i=1;i<=n;i++)cin>>a[i];
    cout<<dfs(0,1,0);
    return 0;
}