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#include <iostream>
#include <algorithm>

using namespace std;

const int MAX_POWER = 250 * 1000;

int N;
int POWERS[MAX_POWER];

int main()
{
	ios_base::sync_with_stdio(false);

	cin >> N;
	for (int i = 0; i < N; i++)
	{
		int a; cin >> a;
		POWERS[a]++;
	}

	int _max = 0;
	for (int i = 0; i < MAX_POWER - 3; i++)
	{
		if (POWERS[i] > 0)
			_max = i;
		POWERS[i + 1] += (POWERS[i]/2);
	}

	cout << _max;
	return 0;
}