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#include <iostream>

using namespace std;

bool coins[202000];
int _max = -1;

void addCoin(int value) {
  while (coins[value] == 1) {
    coins[value] = 0;
    value++;
  }
  coins[value] = 1;
  _max = max(_max, value);
}

int main() {
  ios_base::sync_with_stdio(0);

  int n;
  cin >> n;

  int coin;
  for (int i = 0; i < n; i++) {
    cin >> coin;
    addCoin(coin);
  }

  cout << _max << "\n";
}