Guess the data structure kattis problem

guessthedatastructure.py

import sys
for i in sys.stdin:
    if i.rstrip() == '':
        break

    i = int(i)
    
    s = []
    q = []
    pq = []

    p = [1]*3

    for j in range(i):
        a, b = list(map(int, input().split()))
        if a == 1:
            s.append(b)
            q.append(b)
            pq.append(b)
        else:
            if p[0] == 1:
                if s:
                    if s[len(s)-1] != b:
                        p[0] = 0
                    else:
                        del s[len(s)-1]
                else:
                    p[0] = 0
            if p[1] == 1:
                if q:
                    if q[0] != b:
                        p[1] = 0
                    else:
                        del q[0]
                else:
                    p[1] = 0
            if p[2] == 1:
                if pq:
                    if max(pq) != b:
                        p[2] = 0
                    else:
                        del pq[pq.index(max(pq))]
                else:
                    p[2] = 0

    count = sum(p)

    if count > 1:
        print('not sure')
    elif count == 0:
        print('impossible')
    else:
        if p[0] == 1:
            print('stack')
        else:
            print('queue') if p[1] == 1 else print('priority queue')