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 JAVA):

Solution:
import java.io.*;
import java.util.*;

class Main{
	public static void main(String[] args) throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		PrintWriter pw = new PrintWriter(System.out);
		String[] str = br.readLine().split(" ");
		int n = Integer.parseInt(str[0]);
		str = br.readLine().split(" ");
		int k = Integer.parseInt(str[0]);
		int[] c = new int[k];
		int[] d = new int[k];
		for(int i = 0; i < k; i++){
			int b = Integer.parseInt(str[i + 1]);
			int pow2 = 1;
			for(int j = 0; j < b; j++) pow2 *= 2;
			c[i] = pow2;
			d[i] = b;
		}
		for(int i = 0; i < (1 << k); i++){
			int sum = 0;
			ArrayList<Integer> a = new ArrayList<Integer>();
			for(int j = 0; j < k; j++){
				if((i & (1 << j)) != 0){
					sum += c[j];
					a.add(d[j]);
				}
			}
			pw.print(sum + ":");
			if(i > 0) pw.print(" ");
			for(int j = 0; j < a.size(); j++){
				pw.print(a.get(j));
				if(j != a.size() - 1) pw.print(" ");
			}
			pw.print("\n");
		}
		pw.close();
	}
}