Description

Permutations and combinations are commonly used mathematical methods. A combination refers to selecting r elements from n elements (without considering order and with r ≤ n). We can simply understand the n elements as natural numbers 1, 2, ..., n, and choose any r numbers from them.

You are now required to output all combinations using a recursive method.
For example, when n = 5 and r = 3, all combinations are:
1 2 3   1 2 4   1 2 5   1 3 4   1 3 5   1 4 5   2 3 4   2 3 5   2 4 5   3 4 5

Input Format

A single line containing two natural numbers, n and r (1 < n < 21, 1 ≤ r ≤ n).

Output Format

All combinations, with each combination occupying a separate line and the elements within each combination arranged in ascending order. Each element should occupy exactly three character positions. All combinations should also be listed in lexicographical order.

5 3

  1  2  3
  1  2  4
  1  2  5
  1  3  4
  1  3  5
  1  4  5
  2  3  4
  2  3  5
  2  4  5
  3  4  5