class Stack:
def __init__(self):
self.items = []
def push(self, item):
self.items.append(item)
def pop(self):
return self.items.pop()
def top(self):
return self.items[len(self.items)-1]
def size(self):
return len(self.items)
s = Stack()
num = input()
for _ in range(int(num)):
a = input()
if a.split()[0] == 'push':
b = a.split()[1]
s.push(b)
elif a == 'pop':
if s.size() == 0:
print('error')
else:
print(s.pop())
if a == 'top':
if s.size() == 0:
print('error')
else:
print(s.top())