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())