#include <bits/stdc++.h>
/* #include <atcoder/all> */
using namespace std;
/* using namespace atcoder; */
using pint = pair<int, int>;
using ll = long long;
using ull = unsigned long long;
using vll = vector<long long>;
using pll = pair<ll, ll>;
#define FOR(i, begin, end) \
    for (int i = (begin), i##_end_ = (end); i < i##_end_; i++)
#define IFOR(i, begin, end) \
    for (int i = (end)-1, i##_begin_ = (begin); i >= i##_begin_; i--)
#define REP(i, n) FOR(i, 0, n)
#define IREP(i, n) IFOR(i, 0, n)
#define VREP(s, ite) for (auto ite = s.begin(); ite != s.end(); ++ite)
#define FI first
#define SE second
#define ALL(v) v.begin(), v.end()
#define endl "\n"
#define ciosup  \
    cin.tie(0); \
    ios::sync_with_stdio(false);
#define eb emplace_back
#define vint vector<int>
constexpr ll INF = 1e15 + 7LL;
constexpr ll MOD = 1e9 + 7LL;
template <typename T>
istream &operator>>(istream &is, vector<T> &v) {
    for (int i = 0; i < v.size(); ++i) {
        is >> v[i];
    }
    return is;
}
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
    if (v.size() == 0) return os;
    for (int i = 0; i < v.size() - 1; ++i) {
        os << v[i] << " ";
    }
    os << v[v.size() - 1];
    return os;
}


void solve() {
    int n;
    cin >> n;
    vint p(n);
    cin >> p;
    vector<bool> memo(200000+2, true);
    set<int> se;
    REP(i,200000+2) {
        se.insert(i);
    }
    REP(i,n) {
        if (se.find(p[i]) != se.end()) {
            se.erase(p[i]);
        }
        int ans = *se.begin();
        cout << ans << endl;
    }
}

int main() {
    solve();
    char tmp;
    while (cin >> tmp) {
        cin.putback(tmp);
        solve();
    }
}



#include <bits/stdc++.h>
using namespace std;
using ll = long long;
void Yes() {cout << "Yes\n";}
void No() {cout << "No\n";}
void YES() {cout << "YES\n";}
void NO() {cout << "NO\n";}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	set<int> st;
	for (int i = 0; i <= 200000; i++) st.insert(i);

	int n;
	cin >> n;
	while (n--) {
		int p;
		cin >> p;
		st.erase(p);
		cout << *st.begin() << '\n';
	}
}