Untitled

#include <iostream>
#include <stack>
using namespace std;

const int N = 1e5 + 3;
int n,m,a[N],x;

int main(){

    cin >> n >> m;
    stack <int> s;
    for (int i = n; i > 0; i--){
        s.push(i);
    }
    for (int i = 1; i <= m; i++){
        cin >> x;
        s.push(x);
    }
    int i = 0;
    for ( ; i < n; ){
        if (!a[s.top()]){
            cout << s.top() << " ";
            a[s.top()] = -1;
            i++;
        }
        s.pop();
    }
    return 0;
}