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#include <iostream>

using namespace std;

int main()
{
	constexpr int MAX_INDEX = 201740;
	
	ios::sync_with_stdio(0);

	int n;
	cin >> n;
	int arr[MAX_INDEX + 1]{};
	for (int i = 0; i < n; ++i)
	{
		int a;
		cin >> a;
		++arr[a];
	}

	for (int i = 0; i < MAX_INDEX; ++i)
	{
		arr[i + 1] += arr[i] / 2;
	}

	int i = MAX_INDEX;	
	while (arr[i] == 0) --i;

	cout << i << endl;

    return 0;
}