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;

//------------------------------- Libraries --------------------------------//

//------------------------------- Type Names -------------------------------//

using i64 = int_fast64_t;

using seika = string;
//akari : 1D, yukari : 2D, maki : 3D vector
template <class kizuna>
using akari = vector<kizuna>;
template <class yuzuki>
using yukari = akari<akari<yuzuki>>;
template <class tsurumaki>
using maki = akari<yukari<tsurumaki>>;
//akane : ascending order, aoi : decending order
template <class kotonoha>
using akane = priority_queue<kotonoha, akari<kotonoha>, greater<kotonoha>>;
template <class kotonoha>
using aoi = priority_queue<kotonoha>;

//------------------------------- Dubug Functions ---------------------------//
inline void print()
{
    cout << endl;
}
template <typename First, typename... Rest>
void print(const First &first, const Rest &... rest)
{
    cout << first << ' ';
    print(rest...);
}
//------------------------------- Solver ------------------------------------//

void solve()
{
    int n, k, mask = 0;
    cin >> n >> k;
    while (k--)
    {
        int x;
        cin >> x;
        mask |= 1 << x;
    }
    akari<seika> ans;
    for (int s = mask;; s = (s - 1) & mask)
    {
        stringstream ss;
        ss << s << ':';
        for (int i = 0; i < n; i++)
        {
            if (s >> i & 1)
            {
                ss << ' ' << i;
            }
        }
        ss << '\n';
        ans.push_back(ss.str());
        if (s == 0)
        {
            break;
        }
    }
    reverse(ans.begin(), ans.end());
    for (auto &s : ans)
    {
        cout << s;
    }
}

int main()
{
    solve();
    return 0;
}