class Multiset<T> extends java.util.TreeMap<T,Long>{

public Multiset(){

super();

}

public Multiset(java.util.List<T> list){

super();

for(T e: list) this.addOne(e);

}

public long count(Object elm){

return getOrDefault(elm,0L);

}

public void add(T elm, long amount){

if(!this.containsKey(elm)) put(elm, amount);

else replace(elm, get(elm)+amount);

if(this.count(elm)==0) this.remove(elm);

}

public void addOne(T elm){

this.add(elm, 1);

}

public void removeOne(T elm){

this.add(elm, -1);

}

public void removeAll(T elm){

this.add(elm, -this.count(elm));

}

public static<T> Multiset<T> merge(Multiset<T> a, Multiset<T> b){

Multiset<T> c = new Multiset<>();

for(T x: a.keySet()) c.add(x, a.count(x));

for(T y: b.keySet()) c.add(y, b.count(y));

return c;

}

}