I learned from Google AI, but I think I improved upon it :)

import heapq

myheap = [] heapq.heapify(myheap)

Q = int(input()) valid = set()

for _ in range(Q):

command = [int(i) for i in input().split(' ')]

if command[0] == 1:
    heapq.heappush(myheap, command[1])
    valid.add(command[1])
elif command[0] == 2:
    valid.remove(command[1])
elif command[0] == 3:

    while True:
        ans = myheap[0]
        if ans in valid:
            print(ans)
            break
        else:
            heapq.heappop(myheap)