struct DS{
    list<int> lst ;
    unordered_map< int, list<int>::iterator > has ;
    void insert( int x ){
        lst.push_back( x ) ;
        has[x] = --lst.end() ;
    }
    void erase( int x ){
        if(has.find(x)==has.end()){
            cout << "Element not found" << '\n' ;
            return ;
        }
        lst.erase(has[x]);
        has.erase(x) ;
    }
    void print(){
        for(auto itr:lst)
            cout << itr << " " ;
        cout << '\n' ;
    }
};