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#include <bits/stdc++.h>

using namespace std;

void initialize()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
}

template <typename T>
T read()
{
	T x;
	cin >> x;
	return x;
}

template <typename T>
vector <T> read_n(unsigned n)
{
	vector <T> x(n);
	generate(x.begin(), x.end(), read <T>);
	return x;
}

int main()
{
	initialize();
	auto coins = vector <int>(201740);
	auto n = read <int>();
	while (n--)
		coins[read <int>()]++;
	auto result = 0;
	for (auto i = 1; i < int(coins.size()); i++)
	{
		coins[i] += (coins[i - 1] >> 1);
		if (coins[i])
			result = i;
	}
	cout << result << '\n';
	return 0;
}