Problem:
Enumeration of Combinations

Print all combinations which can be made by $k$ different elements from $0, 1, ..., n-1$.

Note that we represent $0, 1, ... n-1$ as 00...0001, 00...0010, 00...0100, ..., 10...0000 in binary respectively and the integer representation of a combination is calculated by bitwise OR of the selected elements.

Input

The input is given in the following format.

$n \; k$

Output

Print the combinations ordered by their decimal integers. Print a combination in the following format.

$d$: $e_0$ $e_1$ ...

Print ':' after the integer value $d$, then print elements $e_i$ in the combination in ascending order. Separate two adjacency elements by a space character.

Constraints

$1 \leq n \leq 18$

$k \leq n$

Sample Input 1

5 3

Sample Output 1

7: 0 1 2
11: 0 1 3
13: 0 2 3
14: 1 2 3
19: 0 1 4
21: 0 2 4
22: 1 2 4
25: 0 3 4
26: 1 3 4
28: 2 3 4

Solution in Ruby (judge verdict: Accepted)

h={};n,k=gets.split.map &:to_i
[*0...n].combination(k){|e|h[e.map{|_|1<<_}.reduce :+]=e}
puts h.sort.map{|k,v|k.to_s+':'+v.map{|e|' %d'%e}*''}