public class Pair<K,V>{
    private K key;
    private V value;
    public Pair(K key,V value){
        this.key=key;
        this.value=value;
    }
    public K getKey(){
        return key;
    }
    public V getValue(){
        return value;
    }
    public void setKey(K key){
        this.key=key;
    }
    public void setValue(V value){
        this.value=value;
    }
    public static <K,V> Pair<V,K> swap(Pair<K,V> pair){
        return new Pair<>(pair.getValue(), pair.getKey());
    }
}