#include<bits/stdc++.h>
#pragma GCC optimize("O1")
#define endl '\n'
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <iterator>
#include <list>
#include <array>
#include <math.h>
#include <algorithm>
#include <queue>
#include <unordered_set>
#define ll long long int

using namespace std;
void speed()
{
    ios_base::sync_with_stdio(false);
}
int main()
{
    speed();
    #ifdef ONLINE_JUDGE
    freopen("prefmex.in", "r", stdin);
    freopen("prefmex.out", "w", stdout);
    #endif
    int n;cin>>n;int tacos;
    set<int>mex;
    for(int i=0;i<n;i++)
    {
        cin>>tacos;
        mex.erase(tacos);
        mex.insert(i);
        cout<<*mex.begin()<<" ";
    }
    return 0;
}