|시간 제한||메모리 제한||제출||정답||맞은 사람||정답 비율|
|2 초||512 MB||6||4||4||80.000%|
Find a sequence of steps of the following kind (if it exists) that would make all elements of any array of real numbers a1, a2, . . . , an equal:
pick k distinct indices b1, b2, . . . , bk (1 ≤ bi ≤ n) and change the values of ab1, ab2, . . . , abk to their arithmetic mean (that is, 1/k (ab1 + ab2 + . . . + abk)) simultaneously.
The only line contains two integers n and k (2 ≤ k ≤ n ≤ 1000; n is divisible by k).
If a required sequence of steps doesn’t exist, display a single integer −1.
Otherwise, display the number of steps in your sequence t (1 ≤ kt ≤ 106), followed by t step descriptions. Each step description must consist of k distinct integers b1, b2, . . . , bk (1 ≤ bi ≤ n).
It can be shown that if a valid sequence of steps exists, a sequence satisfying kt ≤ 106 exists as well.
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