There are N strings arranged in a row. It is known that, for any two adjacent strings, the string to the left is lexicographically smaller than the string to the right. That is, S_1<S_2<...<S_N holds lexicographically, where S_i is the i-th string from the left.

At least how many different characters are contained in S_1,S_2,...,S_N, if the length of S_i is known to be A_i?

Constraints

* 1 \leq N \leq 2\times 10^5
* 1 \leq A_i \leq 10^9
* A_i is an integer.

Input

Input is given from Standard Input in the following format:


N
A_1 A_2 ... A_N


Output

Print the minimum possible number of different characters contained in the strings.

Examples

Input

3
3 2 1


Output

2


Input

5
2 3 2 1 2


Output

2
#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < n; i++)
const int mx = 200005;
int n, a[mx], l, r = mx;

int main(){
	scanf("%d", &n);
	rep(i,n) scanf("%d", a+i);
	while(l+1 < r){
		int mid = (l+r) / 2, hi = 0;
		bool ok = true;
		map<int, int> mp;
		rep(i,n){
			bool t = hi >= a[i];
			hi = a[i];
			if(t && mid == 1) t = ok = false;
			if(t) while(++mp[hi] >= mid) hi--;
			if(!hi) ok = false;
			mp.erase(mp.upper_bound(hi), mp.end());
		}
		(ok ? r : l) = mid;
	}
	printf("%d\n", r);
}