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

int main(){
	int n;
	cin >> n;
	vector<LL> a(n);
	for(int i = 0; i < n; i++){
		cin >> a[i];
	}

	int ok1 = 1;
	for(int i = 1; i < n; i++){
		if(a[i] <= a[i-1]) ok1 = 0;
	}
	if(ok1){
		cout << 1 << '\n';
		return 0;
	}

	int s = 1; // can't
	int e = n + 1; // can

	while(s + 1 < e){
		int m = (s + e) / 2;

		int ok = 1;

		map<int,int> f;
		int len = 0;
		for(int i = 0; i < n; i++){
			if(a[i] > len){
				len = a[i];
			} else {
				while(!f.empty() && f.rbegin()->first >= a[i]){
					f.erase(f.rbegin()->first);
				}
				f[a[i]-1]++;
				int cur = a[i]-1;
				while(f[cur] >= m){
					f.erase(cur);
					cur--;
					f[cur]++;
					if(cur < 0){
						ok = 0;
					}
				}
				if(!ok) break;
				len = a[i];
			}
		}
		if(ok){
			e = m;
		} else {
			s = m;
		}
	}
	cout << e << '\n';
}