#include <bits/stdc++.h>
#define F first
#define S second

using namespace std;

int n;
int arr[1000005];
int dp[1000005];
int ans;

signed main() {
    ios::sync_with_stdio(0), cin.tie(0);
    cin >> n;
    for (int i = 1; i < n; i++) {
        cin >> arr[i];
    }
    fill(dp, dp+n+1, 1e9);
    dp[1] = 0;
    dp[0] = 0;
    for (int i = 1; i < n; i++) {
        if (arr[i]) {
            for (int j = i; j > 0; j--) {
                dp[i+1] = min(dp[j]+1, dp[i+1]);
            }
        }else {
            dp[i+1] = dp[i] + 1;
        }
        ans = max(dp[i+1], ans);
    }
    cout << ans;
    return 0;
}