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#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <vector>

int main()
{
	constexpr int max_n{ 1000000 };
	constexpr int max_a{ 201718 };

	int n;
	std::scanf("%d", &n);

	std::vector<int> a;
	a.resize(n);
	int actual_min_a{ max_a };
	int actual_max_a{ 0 };
	for (int i{ 0 }; i < n; ++i) {
		std::scanf("%d", &(a[i]));
		actual_min_a = std::min(actual_min_a, a[i]);
		actual_max_a = std::max(actual_max_a, a[i]);
	}

	std::vector<int> powers;
	powers.resize(actual_max_a + 1);
	for (int i{ 0 }; i < n; ++i) {
		++powers[a[i]];
	}

	int reminder{ 0 };
	int final_power{ actual_min_a };
	for (; final_power <= actual_max_a; ++final_power) {
		reminder = (powers[final_power] + reminder) / 2;
	}
	while (reminder > 0) {
		reminder /= 2;
		++final_power;
	}
	--final_power;

	std::printf("%d\n", final_power);
}