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;
  cin >> n;
  int k;
  cin >> k;
  int T = 0;
  for (int i = 0; i < k; i++){
    int b;
    cin >> b;
    T |= (1 << b);
  }
  vector<int> t;
  for (int i = 0; i < n; i++){
    if ((T >> i) & 1){
      t.push_back(i);
    }
  }
  for (int i = 0; i < (1 << k); i++){
    int b = 0;
    for (int j = 0; j < k; j++){
      if (i & (1 << j)){
        b += (1 << t[j]);
      }
    }
    cout << b << ':';
    for (int j = 0; j < n; j++){
      if (b & (1 << j)){
        cout << ' ' << j;
      }
    }
    cout << endl;
  }
}