#include <bits/stdc++.h>
using namespace std;
const int N=2e5+10;
int n,k,a[N];
vector<int>ans,tmp;
queue<int>q; 
int main(){
	freopen("hopeicanbeawake.in","r",stdin);
	freopen("hopeicanbeawake.out","w",stdout);
	scanf("%d %d",&n,&k);
	for(int i=1;i<=k;i++){
		scanf("%d",a+i);
	}
	for(int i=1;i<k;i++){
		ans.push_back(a[i]);
		for(int j=a[i-1]+1;j<a[i];j++)q.push(j);
		if(q.size())ans.push_back(q.front()),q.pop();
	}
	while(q.size())tmp.push_back(q.front()),q.pop();
	for(int i=a[k-1]+1;i<=n;i++)tmp.push_back(i);
	for(int i=tmp.size()-1;i>=0;i--)ans.push_back(tmp[i]);
	for(auto v:ans)printf("%d ",v);
	return 0;
}