C++ :

#include <iostream>

using namespace std;
bool vis[10000];
int main() {
    int n,m,x;
    cin>>n>>m;
    while(m--) {
        cin>>x;
        vis[x] = true;
    }
    bool flag = true;
    for(int i =0;i<=n-1;i++){
        if(!vis[i]){
            flag = false;
            cout<<i<<" ";
        }
    }
    if(flag) cout<<n;
    return 0;
}