题解 | #【模板】队列#

class queue:
    def __init__(self) -> None:
        self.items = []

    def push(self, x: int):
        self.items.append(x)

    def pop(self):
        return self.items.pop(0) if self.items else "error"

    def front(self):
        return self.items[0] if self.items else "error"


res = queue()
for count in range(int(input())):
    action = input()
    if action[:4] == "push":
        res.push(int(action.split()[1]))
    elif action == "pop":
        print(res.pop())
    else:
        print(res.front())