deque

SIZE_LIMIT = 'Дек переполнен'
EMPTY = 'Элементы в Деке отсутсвуют'


class Deque:
    def __init__(self, max_size):
        self._elements = [None] * max_size
        self._max_size = max_size
        self._head = 0
        self._tail = 0
        self._size = 0

    def is_empty(self):
        return self._size == 0

    def size_limit(self):
        return self._size != self._max_size

    def push_back(self, value):
        if not self.size_limit():
            raise IndexError(SIZE_LIMIT)
        self._elements[self._tail] = value
        self._tail = (self._tail + 1) % self._max_size
        self._size += 1

    def push_front(self, value):
        if not self.size_limit():
            raise IndexError(SIZE_LIMIT)
        self._elements[self._head - 1] = value
        self._head = (self._head - 1) % self._max_size
        self._size += 1

    def pop_back(self):
        if self.is_empty():
            raise IndexError(EMPTY)
        x = self._elements[self._tail - 1]
        self._elements[self._tail - 1] = None
        self._tail = (self._tail - 1) % self._max_size
        self._size -= 1
        return x

    def pop_front(self):
        if self.is_empty():
            raise IndexError(EMPTY)
        x = self._elements[self._head]
        self._elements[self._head] = None
        self._head = (self._head + 1) % self._max_size
        self._size -= 1
        return x


def deque(count_command, max_size):
    deque = Deque(max_size)
    output = []
    commands_list = {
        'push_front': deque.push_front,
        'push_back': deque.push_back,
        'pop_front': deque.pop_front,
        'pop_back': deque.pop_back,
    }

    for _ in range(count_command):
        commands = input()
        command, *value = commands.split()
        if value:
            try:
                result = commands_list[command](int(*value))
                if result is not None:
                    output.append(result)
            except IndexError:
                output.append('error')
        else:
            try:
                result = commands_list[command]()
                output.append(result)
            except IndexError:
                output.append('error')
    for result in output:
        print(result)


if __name__ == '__main__':
    count_command = int(input())
    max_size = int(input())
    deque(count_command, max_size)