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#include <iostream>
#include <string>
#include <stdlib.h>
#include <algorithm>
#include <vector>

using namespace std;

struct greaterDesc
{
	template<class T>
	bool operator()(T const &a, T const &b) const { return a > b; }
};

int GetHighestPowerOf2(vector<int> v)
{
	if (v.size() == 1)
	{
		return v[0];
	}

	sort(v.begin(), v.end(), greaterDesc());
	
	bool _continue = true;
	bool _checkNext = true;
	int cutNumbers = 0;

	while (_continue)
	{
		_continue = false;
		vector<int> temp(0);

		for (int i = 0; i < v.size(); ++i)
		{
			if (i == v.size() - 1)
			{
				if (_checkNext)
				{
					temp.push_back(v[i]);
					continue;
				}
			}
			if (_checkNext)
			{
				if (v[i] == v[i + 1])
				{
					temp.push_back(v[i] + 1);
					_continue = true;
					_checkNext = false;
				}
				else
				{
					temp.push_back(v[i]);
					_checkNext = true;
				}
			}
			else
			{
				_checkNext = true;
			}
		}
		v = temp;
	}
	return v[0];
	
}

int main()
{
	int n;
	cin >> n;
	vector<int> v(n);
	for (int i = 0; i<n; ++i) {
		cin >> v[i];
	}
	cout << GetHighestPowerOf2(v);
}