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#include <iostream>

using namespace std;

const int ZAKRES = 300000;
int n, nominal, nominaly[ZAKRES];

int main()
{
	ios_base::sync_with_stdio(0);
	
	cin >> n;
	
	for (int i = 0; i < n; ++i)
	{
		cin >> nominal;
		nominaly[nominal]++;
	}
	
	for (int i = 1; i < ZAKRES; ++i)
	{
		nominaly[i] += nominaly[i - 1] / 2;
		nominaly[i - 1] %= 2;
	}
	
	for (int i = ZAKRES - 1; i >= 0; --i)
	{
		if(nominaly[i] != 0)
		{
			cout << i << endl;
			break;
		}
	}
	
	return 0;
}