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#include <iostream>

#define ARRAY_SIZE 201750

int main()
{
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(0);

	int n;

	std::cin >> n;

	bool *array = new bool[ARRAY_SIZE]();

	for (int i = 0; i < n; i++)
	{
		int temp;
		std::cin >> temp;

		while (true)
		{
			array[temp] = !array[temp];

			if (!array[temp])
			{
				temp++;
			}
			else
			{
				break;
			}
		}
	}

	for (int i = ARRAY_SIZE - 1; i >= 0; i--)
	{
		if (array[i])
		{
			std::cout << i;
			break;
		}
	}

	return 0;
}