#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

const int N = 2e5 + 3, MOD = 998244353;//1e9 + 7;


int32_t main() {

    cin.tie(0);cin.sync_with_stdio(0);
    cout.tie(0);cout.sync_with_stdio(0);

    int n ;
    cin >> n;

    int ans= 1 ;

    vector<int> a(n-1) ;

    for(int i = 2; i <= n; i++) cin >> a[i-2] ;

    vector<int> z;

    z.push_back(1) ;

    for(int i =2 ; i <= n; i++) if(!a[i-2]) z.push_back(i) ;

    if(z.empty() == 0) ans = max(ans , min(z.back() - z[0] , 2) ) ;

    int mx_s =0 ;
    while ( !a.empty() && a.back() == 0 ) mx_s++ , a.pop_back() ;

    if(!a.empty())
    {
        mx_s++ ;
    }

    ans = max(ans , mx_s) ;

    cout << ans ;

    return 0;
}