#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
const int mod = 1e9 + 7;
int n, a[N];
long long ans;
map<long long, int> cnt;
void go(long long pos) {
  cnt[pos]++;
  if (cnt[pos] == 2) {
    cnt[pos] = 0;
    go(pos + 1);
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    go(a[i]);
  }
  for (auto i : cnt) ans = i.first;
  ans++;
  for (auto i : cnt)
    if (i.second == 1) ans--;
  cout << ans;
  return 0;
}
