import sys
from itertools import islice


def window(iterable, n=2):
    it = iter(iterable)
    result = tuple(islice(it, n))
    if len(result) == n:
        yield result
    for elem in it:
        result = result[1:] + (elem,)
        yield result


class rolling_window(object):
    def __init__(self, iterable, n):
        self.iterable = iterable
        self.n = n

    def __iter__(self):
        return window(self.iterable, self.n)


exec(sys.stdin.read())
-----------------------------------------------------------------------------------------------------------------
import sys


def rolling_window(iterable, width):
    class InnerGen:
        def __init__(self, iterable, width):
            self.iterable = iterable
            self.width = width
            self.buffer = []
            self.iterator = self.iterable.__iter__()

        def __iter__(self):
            return self

        def __next__(self):
            try:
                self.buffer = self.buffer[1:]
                while len(self.buffer) < width:
                    self.buffer.append(self.iterator.__next__())
                return tuple(self.buffer)
            except:
                self.iterator = self.iterable.__iter__()
                raise StopIteration()

    return InnerGen(iterable, width)

exec(sys.stdin.read())