#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#define N 200005
using namespace std;
int n;
int a[N];
int main(){
 scanf("%d",&n);
 for(int i=2;i<=n;i++){
  scanf("%d",a+i);
 }a[1]=0;
 int pos=0;
 for(int i=n;i>=1;i--){
  if(a[i]==1){pos=i;break;}
 }
 if(pos==0){printf("%d\n",n-1);return 0;}
 int cnt=0;
 for(int i=1;i<pos;i++)if(a[i]==0)cnt++;
 int ans=1;
 if(pos<=n-1&&pos!=1)ans=max(ans,n-pos+1);
 if(pos<=n-1)ans=max(ans,n-pos);
 int nl=0,nr=0;
 for(int i=pos;i>=1;i--){if(a[i]==0){nr=i;break;}}
 for(int i=1;i<=pos;i++){if(a[i]==0){nl=i;break;}}
 if(cnt>=2&&nr!=nl+1)ans=max(ans,2);
 cout<<ans<<endl;
}