#include <bits/stdc++.h>
using namespace std;
void dbg_out() { cerr << "\b\b]\n"; }
template <typename Head, typename... Tail>
void dbg_out(Head H, Tail... T) {
  cerr << H << ", ";
  dbg_out(T...);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int n;
  cin >> n;
  map<long long, int> cnts;
  for (int i = 0; i < n; ++i) {
    long long x;
    cin >> x;
    cnts[x]++;
  }
  long long ans = 0, curr = 0, cnt = 0;
  for (auto i : cnts) {
    long long a = i.first, b = i.second;
    if (curr == a) {
      if (cnt & 1) cnt++, ans++;
      cnt = b - 1 + cnt / 2;
      curr++;
      continue;
    }
    while (curr < a and cnt) {
      if (cnt & 1) {
        ans++;
        cnt++;
      }
      cnt /= 2;
      cnt--;
      curr++;
    }
    if (curr < a) {
      ans += (a - curr);
      curr = a;
    }
    if (cnt & 1) cnt++, ans++;
    cnt = b - 1 + cnt / 2;
    curr++;
  }
  while (cnt) {
    if (cnt & 1) {
      ans++;
      cnt++;
    }
    cnt /= 2;
    cnt--;
  }
  cout << ans;
  return 0;
}
