/*#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;*/
#include<algorithm>
#include <bits/stdc++.h>
#include<stdio.h>
#include<math.h>
#include<string.h>
#include<stdlib.h>
#include<stdbool.h>
#include<ctype.h>
using namespace std;
#define pb push_back
#define mp make_pair
#define S second
#define F first
#define vi vector<ll>
#define pii pair<ll,ll>
#define bc __builtin_popcountll
#define vvi vector<vi> 
#define vpii vector<pair<ll,ll>>
#define mll unordered_map<ll,ll>
#define INF LONG_LONG_MAX
#define NINF LONG_LONG_MIN
#define fo(i,a,b) for(ll i=a;i<=b;i++)
#define f(i,n) for(ll i=0;i<n;i++)
#define f1(i,n) for(ll i=1;i<=n;i++)
#define fb(i,n) for(ll i=n-1;i>=0;i--)
#define fb1(i,n) for(ll i=n;i>0;i--)
#define endd cout<<'\n';
#define deb(x) cout << #x << "=" << x << endl
#define deb2(x, y) cout << #x << "=" << x << "," << #y << "=" << y << endl
#define fr(it, a) for(auto it = a.begin(); it != a.end(); it++)
#define PI 3.1415926535897932384626
#define clr(x) memset(x, 0, sizeof(x))
#define sortall(x) sort(all(x))
#define all(x) x.begin(), x.end()
#define fast ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define CASES  ll t;cin>>t;while(t--)
typedef long long ll;
typedef unsigned long long ull;
//typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> indexed_set;
//typedef tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
//*X.find_by_order()-->returns an iterator to the k-th largest element (counting from zero)
//X.order_of_key()-->the number of items in a set that are strictly smaller than our item.
struct cmp
{
	bool operator() (ll a,ll b){
		return (a>b);
	}
};
ll ceil(const ll &a, const ll &b)
{
    if(a%b == 0)
        return a/b;
    return a/b +1;
}
ll mod=1000000007;
const ll N=200005;
int main()
{
fast;
    set<ll>s;
    f(i,N)
    {
        s.insert(i);
    }
    ll n;
    cin>>n;
    ll a[n];
    f(i,n)
    {
        cin>>a[i];
        if(s.find(a[i])!=s.end())
        {
            s.erase(a[i]);
        }
        auto it=s.begin();
        cout<<*it;
        endd;
    }
    
    return 0;
}

/**
*   author:  akifpathan
*   created: Saturday 10.10.2020 06:06:06 PM
**/

/*
#pragma GCC optimize("Ofast")
//#pragma GCC optimize ("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
*/

#ifdef LOCAL
#include "debug.h"
#else
#include<bits/stdc++.h>
using namespace std;
#define debug(x...)
#endif
 
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<class T> 
using ordered_set= tree<T, null_type, 
		less<T>, 
		rb_tree_tag, tree_order_statistics_node_update> ;
template<class T> 		
using ordered_mset= tree<T, null_type, 
		less_equal<T>, 
		rb_tree_tag, tree_order_statistics_node_update> ;
		
*/
 
/*
 
PBDS
-------------------------------------------------
			0 based indexing
-------------------------------------------------			 
1) insert(value)
2) erase(value)
3) order_of_key(value) // Number of items strictly smaller than value
4) *find_by_order(k) : K-th element in a set (counting from zero)
 
*/
 
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
 
//mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());	

void solve()
{
	int n;
	cin>>n;
	
	vector<int>vec(n);
	for(int &x: vec) cin>>x;
	
	set<int>st;
	for(int i=0;i<2e5+5;i++) st.insert(i);
	
	for(int x: vec)
	{
		if(st.find(x)!=st.end()) st.erase(x);
		cout<<*(st.begin())<<"\n";
	}
}		

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	
	int testcase=1;
	//cin>>testcase;
	
	for(int i=1;i<=testcase;i++)
	{
		//cout<<"Case "<<i<<": ";
		solve();
	}
	
	#ifdef LOCAL
	cerr<<"\nTime elapsed: " << 1000.0 * clock() / CLOCKS_PER_SEC << " ms\n";
	#endif
	
	
	return 0;
}

