#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<vector>
#include<queue>
#include<map>
#include<bitset>
#include<set>
#define N (200010)
#define P ()
#define M ()
#define inf (0x7f7f7f7f)
#define rg register int
#define Label puts("NAIVE")
#define spa print(' ')
#define ent print('\n')
#define rand() (((rand())<<(15))^(rand()))
#define file(s) freopen(s".in","r",stdin),freopen(s".out","w",stdout)
typedef long double ld;
typedef long long LL;
typedef unsigned long long ull;
using namespace std;
namespace fastIO1{
	inline char read(){
		static const int IN_LEN=1000000;
		static char buf[IN_LEN],*s,*t;
		return (s==t?t=(s=buf)+fread(buf,1,IN_LEN,stdin),(s==t?-1:*s++):*s++);
	}
	template<class T>
	inline void read(T &x){
		static bool iosig;
		static char c;
		for(iosig=false,c=read();!isdigit(c);c=read()){
			if(c=='-')iosig=true;
			if(c==-1)return;
		}
		for(x=0;isdigit(c);c=read())x=((x+(x<<2))<<1)+(c^'0');
		if(iosig)x=-x;
	}
	inline char readc(char &c){
		for(c=read();!isalpha(c)&&!isdigit(c);c=read())
		if(c==-1)return 0;
	}
	const int OUT_LEN = 10000000;
	char obuf[OUT_LEN],*ooh=obuf;
	inline void print(char c){
		if(ooh==obuf+OUT_LEN)fwrite(obuf,1,OUT_LEN,stdout),ooh=obuf;
		*ooh++=c;
	}
	template<class T>
	inline void print(T x){
		static int buf[30],cnt;
		if(x==0)print('0');
		else{
			if(x<0)print('-'),x=-x;
			for(cnt=0;x;x/=10)buf[++cnt]=x%10+48;
			while(cnt)print((char)buf[cnt--]);
		}
	}
	inline void flush(){fwrite(obuf,1,ooh-obuf,stdout);}
}
namespace fastIO2{
	template<class T>
	inline void read(T &x){
		static bool iosig;
		static char c;
		for(iosig=false,c=getchar();!isdigit(c);c=getchar()){
			if(c=='-')iosig=true;
			if(c==-1)return;
		}
		for(x=0;isdigit(c);c=getchar())x=((x+(x<<2))<<1)+(c^'0');
		if(iosig)x=-x;
	}
}
using namespace fastIO1;
#define mkp make_pair
int n,ans,a[N]; set<pair<int,int> > S;
typedef set<pair<int,int> >::iterator iter;
int getpre(iter x){
	if(x==S.begin())return -1;
	x--; return x->second;
}
void add(iter x,int nxt){
	int k=x->second,q=getpre(x);
//	cout<<k<<endl;
	if(x->first==nxt-1){
		S.erase(x);
		if(k+1!=q)S.insert(mkp(nxt-1,k+1));
	}
	else S.insert(mkp(nxt-1,k+1));
}
bool solve(int t){
//	printf("START %d\n",t);
//	cout<<t<<endl;
	S.clear(),S.insert(mkp(1,1));
	for(int i=2;i<=n;i++){
		if(a[i-1]<a[i]){
			iter it=S.end(); it--;
			if(it->second!=1)S.insert(mkp(a[i-1]+1,1));
		}
		else{
			iter it=S.upper_bound(mkp(a[i]+1,0));
			iter x=it; x--;
//			printf(">> (%d,%d)\n",x->first,x->second);
			for(iter j=it;it!=S.end();it=j)j++,S.erase(it),it=j;
			if(x->second==t){
				
				if(S.size()==1)return 0;
				iter y=x; int p=x->first; 
				y--;
//				if(y->second==t)puts("ggg");
//				if(t==26)printf(">> id=%d,len=%d (%d,%d) (%d,%d)\n",i,a[i],x->first,x->second,y->first,y->second);
				add(y,p),S.erase(x),S.insert(mkp(p,1));
			}
			else add(x,a[i]+1);
		}
//		if(t==26&&n-i<=10){
//			for(iter i=S.begin();i!=S.end();i++)
//			cout<<i->first<<" "<<i->second<<endl;
//			puts("-------------");
//		}
	}
	
	return 1;
}
int main(){
//	freopen("in21.txt","r",stdin);
	read(n); int L=1,R=n;
	for(int i=1;i<=n;i++)read(a[i]);
	while(L<=R){
		int mid=(L+R)>>1;
		if(solve(mid))ans=mid,R=mid-1;
		else L=mid+1;
//		cout<<L<<" "<<R<<endl;
	}
	cout<<ans;
}

Measured memory_bytes: 2048