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// Author: Krzysztof Bochenek
// Email:  kpbochenek@gmail.com
// --------------------------------
#include <stdio.h>
#include <vector>
#include <map>
#include <set>
#include <stack>
#include <math.h>
#include <algorithm>
#include <string>
#include <iostream>
#include <climits>

#define pb push_back
#define mp make_pair

typedef long long int ll;
typedef unsigned long long ull;

using namespace std;

#define rep(i, n) for(int i=0; i<n; ++i)

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

  int n, a;
  vector<int> v;
  cin >> n;

  rep(i, n) {
    cin >> a;
    v.pb(a);
  }

  sort(v.begin(), v.end());

  int answer = 0;

  int prev = -1;
  int count = 0;
  for (auto e: v) {
    answer = e;
    if (prev != e) {
      if (prev == e-1) {
        count = count / 2 + 1;
      } else {
        count = 1;
      }
    } else {
      count++;
    }

    prev = e;
  }
  while (count > 1) {
    count = count / 2;
    answer++;
  }

  cout << answer << endl;

  return 0;
}