#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
void speed()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
}
int used[1000001];
int main()
{
    speed();
    #ifdef ONLINE_JUDGE
    freopen("prefmex.in", "r", stdin);
    freopen("prefmex.out", "w", stdout);
    #endif
    int n,a;
    cin>>n;
    int v=0;
    for(int i=0;i<n;i++)
    {
        cin>>a;
        used[a]=1;
        while(used[v]==1)v++;
        cout<<v<<" ";
    }
    return 0;
}