/// Msaa el 5ra
#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")

#include "bits/stdc++.h"

using namespace std;

#define pb push_back
#define F first
#define S second
#define f(i, a, b)  for(int i = a; i < b; i++)
#define all(a)  a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define sz(x) (int)(x).size()
#define mp(x, y) make_pair(x,y)
#define popCnt(x) (__builtin_popcountll(x))
#define int ll

using ll = long long;
using ii = pair<int, int>;
using ull = unsigned long long;

const int N = 1e5 + 5, LG = 18, MOD = 1e9 + 7;
const long double PI = acos(-1);
const long double EPS = 1e-7;


void doWork() {
    int n;
    cin >> n;
    set<int> st;
    for (int i = 2; i <= n; i++) {
        int x;
        cin >> x;
        if (x)st.insert(i);
    }
    if (st.empty()) {
        cout << n - 1 << endl;
        return;
    }
    int mx = 0;
    for (int i = 2; i <= n; i++) {
        auto it = st.lower_bound(i);
        int mn = INT_MAX;
        if (it != st.end())mn = min(mn, *it - i);
        if (it != st.begin())mn = min(mn, i - *prev(it));
        mx = max(mx, mn);
    }
    cout << mx + 1 << endl;
}

int32_t main() {
#ifdef ONLINE_JUDGE
    ios_base::sync_with_stdio(0);
    cin.tie(0);
#endif // ONLINE_JUDGE

    int t = 1;
//    cin >> t;
    while (t--) {
        doWork();
    }
}