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#include <iostream>

using namespace std;

int
main ()
{
  int n, a, max, res, i;
  int coins[201739];		// 201718 + 20 (2^20 > 1mln) 
  cin >> n;
  
  for(i=0;i<201739;i++)
    coins[i] = 0;
    
  for (i = 0; i < n; i++)
    {
      cin >> a;
      if (max < a)
	max = a;
      coins[a]++;
    }
  for (i = 0; i < (max + 20); i++)
    {
      if (i >= max && coins[i] == 1)
	{
	  res = i;
	  break;
	}
      coins[i + 1] += (int) coins[i] / 2;
    }

  cout << res << endl;

  return 0;
}