N = 100010
s = [0]*N
tt = 0
def push(x):
global tt
tt += 1
s[tt] = x
def pop():
global tt
val = s[tt]
tt -= 1
return val
def empty():
global tt
return "NO" if tt > 0 else "YES"
def query():
global tt
return s[tt]
m = int(input())
while m:
m -= 1
li = input().split()
op = li[0]
if op == 'push':
push(int(li[1]))
elif op == 'pop':
pop()
elif op == 'query':
print(query())
elif op == 'empty':
print(empty()