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#include <iostream>

#define MAX_SIZE 2100000

using namespace std;

int T[MAX_SIZE];

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int N;
	cin >> N;

	for (int i = 0; i < MAX_SIZE; i++)
	{
		T[i] = 0;
	}
	

	for (int i = 0; i < N; i++)
	{
		uint64_t a;
		cin >> a;
		T[a]++;
	}
	int w = 0;
	for (int i = 0; i < MAX_SIZE; i++)
	{
		if (T[i] >= 2)
		{
			T[i + 1] += T[i] / 2;
			T[i] %= 2;
		}

		if (T[i] == 1)
		{
			w = i;
		}
	}

	cout << w;

	return 0;
}