#include<bits/stdc++.h>
using namespace std;
int n,m,a[100000],b[100000]={0};
int main(){
    cin>>n>>m;
    for(int i=0;i<m;i++){
    	cin>>a[i];
    }
    for(int i=m-1;i>=0;i--){
    	if(b[a[i]]==0){
    		cout<<a[i]<<" ";
    		b[a[i]]=1;
    	}
    }
    for(int i=1;i<=n;i++){
    	if(b[i]==0){
    		cout<<i<<" ";
    	}
    }
	return 0;
}

/**************************************************************
	Problem: 1527
	User: chenjingqi
	Language: C++
	Result: Accepted
	Time:170 ms
	Memory:2856 kb
****************************************************************/