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 <iostream>
#include <vector>

int main() {
    int N;
    std::cin >> N;

    int m = 0, k;
    std::cin >> k;
    for (int j = 0; j < k; ++j) {
        int i;
        std::cin >> i;
        m += (1 << i);
    }

    std::vector<int> ans;
    for (int b = m; b > 0; b = ((b - 1) & m)) ans.push_back(b);
    ans.push_back(0);

    while (!ans.empty()) {
        int b = ans.back();
        ans.pop_back();

        std::cout << b << ":";
        for (int i = 0; i < N; ++i) {
            if ((b >> i) & 1) std::cout << " " << i;
        }
        std::cout << std::endl;
    }
    return 0;
}