593 B | 593 chars
from sys import stdin
stack = []
n = int(stdin.readline().rstrip())
for i in range(0, n, 1):
order = stdin.readline().rstrip()
if 'push' in order:
order, num = order.split()
stack.append(int(num))
# print(*stack)
elif order == 'pop':
if len(stack) == 0:
print(-1)
else:
print(stack[-1])
stack.pop()
elif order == 'size':
print(len(stack))
elif order == 'top':
if len(stack) == 0:
print(-1)
else :
print(stack[-1])
elif order == 'empty':
if len(stack) == 0:
print(1)
else:
print(0)
# print(order)