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<iostream>
#include<vector>
#include<algorithm>
using namespace std;

int main(){
    int n, k, b;
    cin >> n >> k;

    vector<int> t(k);
    for(int i = 0; i < k; i++)  cin >> t[i];
    sort(t.begin(), t.end());

    for(int i = 0; i < 1<<k; i++){
        int d = 0;
        vector<int> res;
        for(int j = 0; j < k; j++){
            if(i & 1<<j){
                d |= 1<<t[j];
                res.push_back(t[j]);
            }
        }
        cout << d << ":";
        for(int j : res)    cout << " " << j;
        cout << endl;
    }

    return 0;
}