#include <bits/stdc++.h>
using namespace std;
int main(){
  int N;
  cin >> N;
  vector<int> p(N);
  for (int i = 0; i < N; i++){
    cin >> p[i];
  }
  set<int> st;
  for (int i = 0; i <= 200000; i++){
    st.insert(i);
  }
  for (int i = 0; i < N; i++){
    if (st.count(p[i])){
      st.erase(p[i]);
    }
    cout << *st.begin() << endl;
  }
}
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
// --------------------------------------------------------
template<class T> bool chmax(T& a, const T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T& a, const T b) { if (b < a) { a = b; return 1; } return 0; }
#define FOR(i,l,r) for (int i = (l); i < (r); ++i)
#define RFOR(i,l,r) for (int i = (r)-1; (l) <= i; --i)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SORT(c) sort(ALL(c))
#define RSORT(c) sort(RALL(c))
#define MIN(c) *min_element(ALL(c))
#define MAX(c) *max_element(ALL(c))
#define SUM(c) accumulate(ALL(c), 0)
#define SUMLL(c) accumulate(ALL(c), 0LL)
#define SZ(c) ((int)(c).size())
#define CIN(c) cin >> (c)
#define COUT(c) cout << (c) << '\n'
#define debug(x) cerr << #x << " = " << (x) << '\n';
using P = pair<int,int>;
using VP = vector<P>;
using VVP = vector<VP>;
using VS = vector<string>;
using VI = vector<int>;
using VVI = vector<VI>;
using VLL = vector<ll>;
using VVLL = vector<VLL>;
using VB = vector<bool>;
using VVB = vector<VB>;
using VD = vector<double>;
using VVD = vector<VD>;
static const double EPS = 1e-10;
static const double PI  = acos(-1.0);
static const ll MOD = 1000000007;
// static const ll MOD = 998244353;
static const int INF = (1 << 30) - 1;  // 1073741824 - 1
// static const ll INF = (1LL << 62) - 1;  // 4611686018427387904 - 1
// --------------------------------------------------------
// #include <atcoder/all>
// using namespace atcoder;


int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    int N; cin >> N;
    VI P(N); REP(i,N) cin >> P[i];

    const int MAX_P = 2e5;
    VB seen(MAX_P + 2, false);
    int min = 0;
    for (int p : P) {
        seen[p] = true;
        while (seen[min]) { min++; }
        COUT(min);
    }

    return 0;
}
