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,k;cin>>n>>k;
	vector<int> b(n);
	for(int i=0;i<k;++i) cin>>b[i];
	
	for(int bit=0;bit<(1LL<<k);++bit){
		bitset<64> bs(0);
		for(int i=0;i<k;++i){
			if(bit>>i&1) bs.set(b[i]);
		}
		cout<<bs.to_ulong()<<":";
		for(int i=0;i<k;++i){
			if(bit>>i&1) {
				cout<<" "<<b[i];
			}
		}
		cout<<endl;
	}
  return 0;
}