#include<algorithm>
#include<cstdio>
#include<vector>
namespace Input{
	const int BUFFLEN=1<<20;
	char buf[BUFFLEN|2],*p1=buf,*p2=buf;
	inline char getc(){
		if(p1==p2)
			p1=buf,
			p2=buf+fread(buf,1,BUFFLEN,stdin);
		return p1==p2?EOF:*p1++;
	}
	inline bool isdgt(const char op){return op>='0'&&op<='9';}
	long long read(){
		static long long res;static char op,f;
		for(f=0,op=getc();!isdgt(op);op=getc())f|=(op=='-');
		for(res=0;isdgt(op);op=getc())res=res*10+(op^'0');
		return f?-res:res;
	}
}
using namespace std;
typedef long long ll;
const int N=100010;
int s[N],n;
void solve(){
	n=Input::read();
	for(int i=1;i<n;++i)
		s[i]=Input::read();
	int ans=1,lst=0;
	for(int i=1;i<n;++i)
	if(s[i]==0){
		lst++;
	}
	else{
		if(lst>1)
			ans=2;
		else if(lst==1&&i-2>0)
			ans=2;
		lst=0;
	}
	if(lst<n-1)
		ans=max(ans,lst+1);
	else
		ans=n-1;
	printf("%d\n",ans);
}
signed main(int argc,char **argv){
//	freopen("order.in","r",stdin);
//	freopen("order.out","w",stdout);
	int T=1;
	while(T--)solve();
	return 0;
}