#include <bits/stdc++.h>
#include <atcoder/modint>
using namespace std;
using mint = atcoder::static_modint<(int)1e9 + 7>;
template <class F> class y_combinator {
	F f;

  public:
	y_combinator(F&& f) : f(std::forward<F>(f)) {}
	template <class... Args> auto operator()(Args &&... args) const { return f(*this, std::forward<Args>(args)...); }
};
using ll = long long;
using ld = long double;
template <class T, class U = std::less<T>> using prique = std::priority_queue<T, std::vector<T>, U>;
template <class T> T floor(T a, T b) { return a / b - (a % b && (a ^ b) < 0); }
template <class T> T ceil(T a, T b) { return floor(a + b - 1, b); }
template <class T> bool chmin(T& x, const T& y) { return (x > y ? x = y, true : false); }
template <class T> bool chmax(T& x, const T& y) { return (x < y ? x = y, true : false); }
#define overload4(a, b, c, d, e, ...) e
#define rep1(a) for (long long _i = 0; _i < (a); _i++)
#define rep2(i, a) for (long long i = 0; i < (a); i++)
#define rep3(i, a, b) for (long long i = (a); i < (b); i++)
#define rep4(i, a, b, c) for (long long i = (a); i < (b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define rrep(i, a, b, c) for (long long i = (a); i > (b); i += (c))
#define all(x) std::begin(x), std::end(x)
#define rall(x) std::rbegin(x), std::rend(x)
#define pb push_back

int freq[1<<17];
void run_case() {
	int N;
	cin >> N;
	int mx = 0;
	rep(i, N) {
		int a;
		cin >> a;
		freq[a]++;
		mx = max(mx, a);
	}
	int ans = 0;
	while(freq[ans] >= 2) ans++;
	int s = 0;
	rep(i, 1<<17) s += max(0, freq[i]-2);
	if(s > 0) {
		ans += freq[ans] == 1;
		while(freq[ans] >= 2) ans += 1;
		cout << ans << endl;
		return;
	}
	freq[mx]--;
	freq[ans]++;
	while(freq[ans] >= 2) ans += 1;
	cout << ans << endl;
}

int main() {
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(nullptr);
	std::fixed(std::cout).precision(16);
	int T = 1;
	//cin >> T;
	while(T--) run_case();
	return 0;
}