#include <bits/stdc++.h>

using namespace std;

int a,n,b[1000000],j=0;

int mex()
{
    while(b[j]==1)j++;
    return j;
}

int main()
{
#ifdef ONLINE_JUDGE
    freopen("prefmex.in", "r", stdin);
    freopen("prefmex.out", "w", stdout);
#endif // ONLINE_JUDGE

ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
    cin>>n;
    for(int i=0; i<n; i++)
    {
        cin>>a;
        b[a]=1;
        cout<<mex();
        cout<<" ";
    }
    cout<<endl;
    return 0;
}