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;
#define rep(i,n) for(int i=0;i<n;i++)
#define int long long
int n, k;
int a[20];
signed main() {
	cin >> n >> k;
	rep(i, k)cin >> a[i];
	rep(i, (1 << k)) {
		int ans = 0;
		vector<int>v;
		rep(j, n) {
			if ((i >> j) & 1) {
				ans += (1 << a[j]);
				v.push_back(a[j]);
			}
		}
		if (ans == 0)puts("0:");
		else {
			cout << ans << ":";
			for (int x : v)cout << " " << x;
			cout << endl;
		}
	}
	return 0;
}