#include <bits/stdc++.h>
#define int long long

using namespace std;

signed main()
{
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n, o = 1, z = 0, ans = 1;
    cin >> n;
    vector<int> arr(n);
    for( int i=1 ; i < n ; i++ ) cin >> arr[i];
    for( int i=1 ; i < n ; i++ ) {
        if( arr[i] == 1 ) {
            if( z >= 2 ) ans = max(ans, (int)2);
            else ans = max(ans, z);
            z = 1;
        }
        else z++;
    }
    cout << max(ans, z) << '\n';
}