#include<bits/stdc++.h>
#define N 100100
using namespace std;
int n,a[N],ans;
void dfs(int pos,int x,int dep){
	if(pos>1&&x==0) return;
	if(pos>n){ans=max(ans,dep);return;} int newx;
	if(a[pos]==0) newx=0; if(a[pos]==1||a[pos]==2) newx=15;
	if(a[pos]==3||x==4) newx=x-1;  if(a[pos]==5) newx=x;
	if(a[pos]==6) newx=x+1; if(a[pos]==7) newx=x+3;
	dfs(pos*2,newx,dep+1),dfs(pos*2+1,newx,dep+1);
}
int main(){
	freopen("traversal.in","r",stdin),freopen("traversal.out","w",stdout);
	cin>>n; for(int i=1;i<=n;i++) cin>>a[i];
	dfs(1,0,0); cout<<ans<<endl;
}