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#include <iostream>
#include <bitset>
#include <vector>

using namespace std;

// constexpr static const size_t X = 16;
constexpr static const size_t X = 201718 + 200;

void update(bitset<X>& b, size_t i) {
  while (b[i])
    b[i++] = false;
  b[i] = true;
}

int main() {
  ios::sync_with_stdio(false);
  
  int n;
  cin >> n;

  bitset<X> x;
  for (int i = 0; i < n; ++i) {
    int y;
    cin >> y;
    
    update(x, y);
  }

  int b = 0;
  for (int i = X - 1; i >= 0; --i) {
    if (x[i]) {
      b = i;
      break;
    }
  }

  cout << b << '\n';
  return 0;
}