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:
// 失敗するからこそ そこから立ち向かって行く強さがあってそんな強さが本当の強さだと私は思うから
// ぜったいあきらめない
#include<bits/stdc++.h>
using namespace std;

#if defined(DAIJOBU)
#include "/home/ichigo/debug.hpp"
#define deb(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define deb(x...)
#endif
#define FIO {ios::sync_with_stdio(0);cin.tie(nullptr);cout.tie(nullptr);}



int main(){
	FIO
	
	int n;
	cin >> n;
	int k;
	cin >> k;
	int b[n];
	for(int i = 0; i < k; i++)cin >> b[i];
	sort(b, b + k);
	for(int i = 0; i < (1 << k); i++){
		vector<int> now;
		int rep = 0;
		for(int j = 0; j < k; j++){
			if(i & (1 << j))now.push_back(b[j]), rep += pow(2, b[j]);
		}
		cout << rep << ':';
		for(auto j:now)cout << ' ' << j;
		cout << '\n';
	}
	return 0;
}