#Uva problm id: 11995 - I Can Guess the Data Structure!
# https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=3146
while True:
try :
stack=[]
queue=[]
priority_queue=[]
n = int(input())
m=n
f=-1
c=0 #counter of removing elements
s=0 #stack flag
p=0 #priority_queue flag
q=0 #queue flag
while(n):
n=n-1
i,j=input().split()
i=int(i)
j=int(j)
if i==1:
queue.append(j)
stack.append(j)
priority_queue.append(j)
priority_queue.sort(reverse=True)
else:
c=c+1 #counting removing elements
if len(stack)>0 and j==stack[len(stack)-1] and s==0:
stack.pop(len(stack)-1)
else:
s=1
if len(queue)>0 and j==queue[0] and q==0:
queue.pop(0)
else:
q=1
if len(priority_queue)>0 and j==priority_queue[0] and p==0:
priority_queue.pop(0)
else:
p=1
if s==1 and p==1 and q==1:
f=0
if(c>m-c):
f=0
if f!=0:
if (s==0 and p==0 and q==0) or (s==0 and q==0) or (p==0 and q==0) or (s==0 and p==0 ):
print("not sure")
elif m-2*c==len(stack):
print("stack")
elif m-2*c==len(queue):
print("queue")
elif m-2*c==len(priority_queue):
print("priority queue")
else:
print("impossible")
else:
print("impossible")
except EOFError:
break
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