import sys
from collections import deque
def push(X) -> None:
stack.appendleft(X)
def pop() -> None:
if not stack:
print (-1)
else:
print (stack.popleft())
def size() -> None:
print (len(stack))
def empty() -> None:
if not len(stack):
print (1)
else:
print (0)
def top() -> None:
if not stack:
print (-1)
else:
print (stack[0])
if __name__ == "__main__":
N = int(input())
stack = deque()
command_dict = {
'push': push,
'pop' : pop,
'size' : size,
'empty': empty,
'top': top
}
for _ in range(N):
command = sys.stdin.readline().split()
if len(command) > 1:
command_dict[command[0]](int(command[1]))
else:
command_dict[command[0]]()