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 <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#define long long long
#define LF '\n'
#define ALL(x) x.begin(), x.end()
using namespace std;
typedef pair<int,int> pii;
template<class A, class B>inline bool chmax(A &a, const B &b){return b>a ? a=b,1 : 0;}
template<class A, class B>inline bool chmin(A &a, const B &b){return b<a ? a=b,1 : 0;}
constexpr int INF = 0x3f3f3f3f;


signed main()
{
  int N, K;
  int T = 0;

  scanf("%d%d", &N, &K);
  vector<int> e(K);

  for (int i = 0; i < K; ++i) {
    scanf("%d", &e[i]);
  }

  set<int> U;

  for (int i = 0; i < (1<<K); ++i) {
    int ans = 0;
    for (int j = 0; j < K; ++j) {
      if(i & (1<<j)) ans |= (1 << e[j]);
    }
    U.insert(ans);
  }

  for (int e : U) {
    printf("%d:", e);
    for (int i = 0; i < N; ++i) {
      if (e & (1<<i)) printf(" %d", i);
    }
    puts("");
  }

}