#include<bits/stdc++.h>
#define int long long
using namespace std;
void read() {}
template<typename T, typename... T2>
inline void read(T &x, T2 &... oth) {
    x = 0;
    int ch = getchar(), f = 0;
    while(ch < '0' || ch > '9') {
        if(ch == '-') f = 1;
        ch = getchar();
    }
    while(ch >= '0' && ch <= '9') {
        x = (x << 1) + (x << 3) + (ch ^ 48);
        ch = getchar();
    }
    if(f)x = -x;
    read(oth...);
}
inline void write(int a) {
    if(a < 0) putchar('-'), a = -a;
    if(a >= 10)write(a / 10);
    putchar(a % 10 + 48);
}
void qui(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);cout.tie(nullptr);
}
const int maxn=1e5+500;
bool flag[maxn];
int n,m,a[maxn],b[maxn],tot;
signed main(){
	read(n,m);
	for(int i=1;i<=m;i++)
		read(a[i]),flag[a[i]]=true;
	for(int i=1;i<=n;i++)
	if(!flag[i])b[++tot]=i;
	int k1=1,k2=1;
	while(k1<=m||k2<=tot){
		if(k2>tot){
			printf("%lld ",a[k1++]);
			continue;
		}
		if(k1>m){
			printf("%lld ",b[k2++]);
			continue;
		}
		if(a[k1]<b[k2]) printf("%lld ",a[k1++]);
		else printf("%lld ",b[k2++]);
	}
    return 0;
}