Problem: You are given a set $T$, which is a subset of $S$. The set $S$ consists of $0, 1, ... n-1$. Print all subsets of $T$. 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 subset is calculated by bitwise OR of existing elements.

Constraints

* $1 \leq n \leq 28$
* $0 \leq k \leq 18$
* $k \leq n$
* $0 \leq b_i < n$

Input

The input is given in the following format.


$n$
$k \; b_0 \; b_1 \; ... \; b_{k-1}$


$k$ is the number of elements in $T$, and $b_i$ represents elements in $T$.

Output

Print the subsets ordered by their decimal integers. Print a subset in the following format.


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


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

Example

Input

4
2 0 2


Output

0:
1: 0
4: 2
5: 0 2

Solution (in CPP):

Solution:
#include <cstdio>
int main()
{
	int n, k;
	int b[18];
    scanf("%d %d",&n,&k);
	for(int i=0;i<k;i++)
	    scanf("%d",&b[i]);
	for(long j=0;j<(1<<k);j++) {
		long d=0;
		for(int u=0;u<k;u++) {
			if(j&(1<<u))
				d+=(1<< b[u]);
		}
		printf("%d:",d);
		for(int s=0;s<k;s++){
			if(j&(1<<s))
				printf(" %d",b[s]);
		}
		printf("\n");
	}
	return 0;
}