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#include <iostream>

using namespace std;

const int MAXN = 1e6+5;
int bucket[MAXN];
int main()
{
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  for (int i = 0; i < n; i++)
  {
    int a;
    cin >> a;
    bucket[a]++;
  }

  int res = 0;
  for (int i = 0; i <= 300*1000; i++)
  {
    if (bucket[i]) res = i;
    bucket[i+1] += bucket[i]/2;
  }
  cout << res << "\n";
}