#include<cstdio>
#include<algorithm>
#include<map>
using namespace std;
int n, w[201000];
map<int, int>Map;
bool Pos(int K) {
	int i;
	Map.clear();
	for (i = 2; i <= n; i++) {
		if (w[i] > w[i - 1]) {
			continue;
		}
		while (!Map.empty()) {
			auto it = Map.end();
			it--;
			if (it->first <= w[i])break;
			Map.erase(it);
		}
		Map[w[i]]++;
		int pv = w[i];
		while(Map[pv] == K) {
			if (pv == 1)return false;
			Map[pv] -= K;
			pv--;
			Map[pv]++;
		}
	}
	return true;
}
int main() {
	int i, chk = 0;
	scanf("%d", &n);
	for (i = 1; i <= n; i++) {
		scanf("%d", &w[i]);
		if (i>1 && w[i] <= w[i - 1])chk = 1;
	}
	if (!chk) {
		puts("1");
		return 0;
	}
	int b = 2, e = n, mid, r = 0;
	while (b <= e) {
		mid = (b + e) >> 1;
		if (Pos(mid)) {
			r = mid;
			e = mid - 1;
		}
		else b = mid + 1;
	}
	printf("%d\n", r);
}