#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long 

const int maxn = 200050;
const int inf = 0x3f3f3f3f3f3f3f3f;

int n, a[maxn];

void solve() {
    cin >> n;
    int cnt = 0;
    for(int i = 2; i <= n; i++) {
         cin >> a[i];
         cnt += a[i];
    }
    if(cnt == n - 2 && a[2] == 0) {
        cout << 1;
        return;
    }
    int ans = 1;
    for(int i = 2; i <= n; i++) {
        if(a[i] == 1) continue;
        int j = i;
        while(j + 1 <= n && a[j + 1] == 0) {
            j++;
        }
        int cost;
        if(j == n) {
            cost = j - i + 1 + a[i - 1];
        } else {
            cost = 2;
        }
        ans = max(ans, cost);
        i = j;
    }
    cout << ans;
}

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    int t = 1;
    while(t--) solve();
}