#include <iostream>
#include <stack>
#include <vector>
#include <math.h>
using namespace std;
 
int main ()
{
	int n;
	cin>>n;
	vector <long> arr;
	vector <long> left (1000005, 0);
	vector <long> right (1000005, 0);
	arr.push_back(0);
	for (int i=1; i<=n; i++)
	{
		long tmp;
		cin>>tmp;
		arr.push_back (tmp);
	}
	arr.push_back(0);
	
	stack <int> SL;
	SL.push(0);
	for (int i=1; i<=n; i++)
	{
		while (!SL.empty() && arr[SL.top()]>=arr[i]) SL.pop();
		if (!SL.empty()) left[i]=SL.top();
		SL.push(i);
	}
	
	stack <int> SR;
	SR.push(n+1);
	for (int i=n; i>=1; i--)
	{
		while (!SR.empty() && arr[SR.top()]>=arr[i]) SR.pop();
		if (!SR.empty()) right[i]=SR.top();
		SR.push(i);
	}
	long Ans=0;
	for (int i=1; i<=n; i++)
	{
		if (right[i]-left[i]-1 >= arr[i]) Ans = max (Ans, arr[i]);
	}
	cout<<Ans;
	return 0;
}