#include<bits/stdc++.h>
using namespace std;
#define int long long
#define PII pair<int,int>
#define fi first
#define se second
const int N=2e5+10;
int a[N],n;
bool check(int x)
{
	if(x==1)
	{
		for(int i=1;i<n;i++)if(a[i]>=a[i+1])return 0;
		return 1;
	}
	vector<PII>stk;int len=0;
	for(int i=1;i<=n;i++)
	{
		if(a[i]>len)len=a[i];
		else if(a[i]==len)
		{
			int id=len;
			while(!stk.empty()&&stk.back().fi==id&&stk.back().se==x-1)stk.pop_back(),id--;
			if(id==0)return 0;
			if(!stk.empty()&&stk.back().fi==id)
			{
				int x=stk.back().se;
				stk.pop_back();stk.push_back({id,x+1});
			}
			else stk.push_back({id,1});
		}
		else
		{
			while(!stk.empty()&&stk.back().fi>a[i])stk.pop_back();
			int id=a[i];
			while(!stk.empty()&&stk.back().fi==id&&stk.back().se==x-1)stk.pop_back(),id--;
			if(id==0)return 0;
			if(!stk.empty()&&stk.back().fi==id)
			{
				int x=stk.back().se;
				stk.pop_back();stk.push_back({id,x+1});
			}
			else stk.push_back({id,1});
		}
		len=a[i];
	}
	return 1;
}
signed main()
{
	cin>>n;
	for(int i=1;i<=n;i++)cin>>a[i];
	int l=1,r=1e9,ans=1e9;
	while(l<=r)
	{
		int mid=(l+r)>>1;
		if(check(mid))r=mid-1,ans=mid;
		else l=mid+1;
	}
	cout<<ans;
	return 0;
}