#include <bits/stdc++.h>
using namespace std;

const int MN = 1e6 + 6;

int n,a,t;
bool b[MN];

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);
	
	freopen("prefmex.in", "r", stdin);
	freopen("prefmex.out", "w", stdout);
	
	cin>>n;
	t=0;
	
	for(int i=1;i<=n;i++){
		cin>>a;
		b[a]=1;
		if(a!=t)cout<<t<<" ";
		else{
			for(int i=a+1;i<=1e6;i++){
				if(b[i]==0){
					t=i;
					break;
				}
			}
			cout<<t<<" ";
		}
	}
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	return 0;
}