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

#define int long long
#define double long double

#define pii pair<int, int>

struct Fenwick {
	vector<int> v;

	Fenwick(int n) : v(n + 1) {
	}

	void add(int i, int x) {
		i++;
		for (int j = i; j < v.size(); j += j & -j) {
			v[j] += x;
		}
	}

	int sum(int i) {
		i++;
		int x = 0;
		for (int j = i; j > 0; j -= j & -j) {
			x += v[j];
		}
		return x;
	}
};

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
#ifdef CB
	freopen("be2.txt", "r", stdin);
//	freopen("out.txt", "w", stdout);
#endif
	int N;
	cin >> N;
	vector<int> v(N);
	for (int i = 0; i < N; i++) {
		cin >> v[i];
	}
	int l = 0, h = N;
	while (l < h) {
		int m = (l + h) / 2;
		Fenwick f(N * 2);
		bool ok = true;
		for (int i = 0; i < N; i++) {
			f.add(v[i], 1);
			f.add(v[i] + m + 1, -1);
			if (!f.sum(i) && !f.sum(N + i)) {
				ok = false;
				break;
			}
		}
		if (!ok) {
			l = m + 1;
		}
		else {
			h = m;
		}
	}
	cout << l << '\n';
	return 0;
}