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:
#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
#define max0(a,b,c) max(max(a,b),c)
#define min0(a,b,c) min(min(a,b),c)
#define ft first
#define sc second
#define pb push_back
#define all(v) (v).begin(),(v).end()
#define mod 1000000007
using namespace std;
using Graph = vector<vector<int>>;
typedef long long lint;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ldouble;
typedef vector<int> vec;
typedef vector<ll> lvec;
typedef vector<ull> ulvec;
typedef vector<double> dvec;
typedef vector<pair<int,int>> pvec;
typedef vector<pair<ll,ll>> plvec;
typedef vector<tuple<ll,ll,ll>> tvec;
typedef vector<string> svec;

int main(){
    int n;
    cin>>n;
    int k;
    cin>>k;
    vec a(k);
    rep(i,k) cin>>a[i];
    for(int i=0;i<(1<<k);i++){
        int cnt=0;
        for(int j=0;j<n;j++){
            for(int m=0;m<k;m++){
                if((i>>m&1)&&a[m]==j) cnt+=(int)pow(2,a[m]);
            }
        }
        cout<<cnt<<':';
        for(int j=0;j<k;j++){
            if(i>>j&1) cout<<' '<<a[j];
        }
        cout<<endl;
    }
}