#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <set>
#include <queue>
#include <algorithm>
#include <vector>
#include <cctype>
#include <stack>
#include <sstream>
#include <list>
#include <map>
#include <assert.h>
#define debug() puts("************")
#define MS(a,b) memset(a,b,sizeof a)
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int,int> P;
const int INF = 0x3f3f3f3f;
const double inf = 1e20;
const double PI = 3.1415926535;
const double eps = 1e-15;
const LL mod = 1e9+7;
const int dx[] = {-1,0,1,0};
const int dy[] = {0,1,0,-1};
const int maxn = 200000 + 7, maxd = 100000 + 7;
int n, m;
int vis[maxn];
int a[maxn];
int main() {
scanf("%d %d", &n, &m);
for(int i = 0; i < m; ++i) {
scanf("%d", &a[i]);
}
//cout << " +++++++ " << endl;
printf("%d\n", a[m-1]);
vis[a[m-1]] = 1;
for(int i = m-2; i >= 0; --i) {
if(vis[a[i]] == 0)printf("%d\n", a[i]);
vis[a[i]] = 1;
}
for(int i = 1; i <= n; ++i) {
if(vis[i] == 0) {
printf("%d\n", i);
}
}
return 0;
}
