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#include <iostream>
//#include <fstream>

using namespace std;

int tablica[1000007];

int main()
{
	//fstream plik;
	
	//plik.open("in/in11.in");
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int n, x, my_max = 0, my_max1 = 0, my_max2 = 0;
	bool czynnik = 0;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> x;
		if (x > my_max1)
		{
			my_max1 = x;
		}
		
		tablica[x]++;
	}
	for (int i = 1; i <= my_max1 + 1 || czynnik == 1; i++)
	{
		if (tablica[i] != 0 && i > my_max)
		{
			my_max = i;
		}

		while (tablica[i] > 1)
		{
			tablica[i + 1]++;
			tablica[i]-=2;
		}

		if (tablica[i + 1] > 1)
		{
			czynnik = 1;
		}
		else
		{
			if (tablica[i + 1] != 0 && i + 1 > my_max)
			{
				my_max = i + 1;
			}
			czynnik = 0;
		}
	}

	cout << my_max;
    return 0;
}