#include<bits/stdc++.h>
using namespace std;
	int a[1000099],f[1000099]={0};
int n,m,x,i,j,t;
int main(){

	cin>>n>>m;
	for(int i=1;i<=m;i++) cin>>a[i];
	for(int i=m;i>=1;i--){
		if(f[a[i]]==0){
			cout<<a[i]<<" ";
			f[a[i]]=1;
		}
	}
for(int i=1;i<=n;i++){
	if(f[i]==0){
		cout<<i<<" ";
	}
}
	return 0;
}

/**************************************************************
	Problem: 1527
	User: chenyubo
	Language: C++
	Result: Accepted
	Time:163 ms
	Memory:9888 kb
****************************************************************/