n=
int
(
input
())
l=
[]
for
_
in
range
(
n
):
order=
input
()
if
‘push’
in
order
:
a
,
b=order.split
()
l.append
(
b
)
elif
‘pop’
in
order
:
if
l
:
(
l
[
-1
])
del
l
[
-1
]
else
:
(
-1
)
elif
‘size’
in
order
:
(
len
(
l
))
elif
’empty'
in
order
:
if
l
:
(
0
)
else
:
(
1
)
elif
’top'
in
order
:
if
l
:
(
l
[
-1
])
else
:
(
-1
)