#include <bits/stdc++.h>
using namespace std;

#ifdef DEBUG
#define fast
#else
#define fast cin.tie(0)->sync_with_stdio(0)
#define cerr if(1);else cerr
#define endl '\n'
#endif
#define _ <<' '<<
#define ALL(v) v.begin(),v.end()
#define ft first
#define sd second

using ll = long long;
using ld = long double;
using pii = pair<int,int>;

signed main() {
    fast;

    int n;
    cin >> n;
    vector<int> v(n-1);
    for (auto &x: v) cin >> x;

    int l1 = n-1;
    while (l1-1 >= 0 and v[l1-1] == 0)
        l1--;
    int f0 = 0;
    while (f0 < n-1 and v[f0] == 1)
        f0++;
    cerr _ l1 _ f0 _ endl;

    vector<int> d(n);
    d[0] = 0;
    for (int i = 1; i < n; i++) {
        if (v[i-1] == 1) {
            d[i] = 1;
        } else if (i < l1) {
            d[i] = min(d[i-1]+1, 2);
        } else {
            d[i] = d[i-1] + 1;
        }
    }

    int r = *max_element(ALL(d));
    cout << r << endl;

    return 0;
}