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 <bits/stdc++.h>
using namespace std;

int main(){
	int n;
	scanf("%d", &n);
	int a;
	scanf("%d", &a);
	int mask = 0;
	for(int i = 0; i < a; i++) {
		int t;
		scanf("%d", &t);
		mask |= (1 << t);
	}
	for(int i = mask; ; i = mask & (i - 1)) {
		int k = i ^ mask;
		printf("%d:", k);
		for(int j = 0; j < n; j++) {
			if(k & (1 << j))
				printf(" %d", j);
		}
		printf("\n");
		if(i == 0) break;
	}
}