using System.Collections.Generic;
using System.Linq;

public class PriorityQueue<TElement, TPriority> {
    readonly SortedList<TPriority, Queue<TElement>> priorities = new ();

    public int Count { get; set; }

    public void Enqueue(TElement element, TPriority priority) {
        if (!priorities.ContainsKey(priority)) {
            priorities[priority] = new Queue<TElement>();
        }

        priorities[priority].Enqueue(element);
        Count++;
    }

    public TElement Dequeue() {
        if (priorities.Count == 0) throw new System.InvalidOperationException("The queue is empty");

        var firstPair = priorities.First();
        var element = firstPair.Value.Dequeue();
        if (firstPair.Value.Count == 0) priorities.Remove(firstPair.Key);

        Count--;
        return element;
    }
}