Problem:
Score : 400 points

Problem Statement

Find the largest integer that can be formed with exactly N matchsticks, under the following conditions:

Every digit in the integer must be one of the digits A_1, A_2, ..., A_M (1 \leq A_i \leq 9).

The number of matchsticks used to form digits 1, 2, 3, 4, 5, 6, 7, 8, 9 should be 2, 5, 5, 4, 5, 6, 3, 7, 6, respectively.

Constraints

All values in input are integers.

2 \leq N \leq 10^4

1 \leq M \leq 9

1 \leq A_i \leq 9

A_i are all different.

There exists an integer that can be formed by exactly N matchsticks under the conditions.

Input

Input is given from Standard Input in the following format:

N M
A_1 A_2 ... A_M

Output

Print the largest integer that can be formed with exactly N matchsticks under the conditions in the problem statement.

Sample Input 1

20 4
3 7 8 4

Sample Output 1

777773

The integer 777773 can be formed with 3 + 3 + 3 + 3 + 3 + 5 = 20 matchsticks, and this is the largest integer that can be formed by 20 matchsticks under the conditions.

Sample Input 2

101 9
9 8 7 6 5 4 3 2 1

Sample Output 2

71111111111111111111111111111111111111111111111111

The output may not fit into a 64-bit integer type.

Sample Input 3

15 3
5 4 6

Sample Output 3

654

Solution in Rust (1.15.1) (judge verdict: Accepted)

macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

fn main() {
    input!{
        n: usize,
        m: usize,
        am: [usize; m]
    }
    let match_nums = [6,2,5,5,4,5,6,3,7,6];
    let mut dp: Vec<Answer> = vec![None; n + 1];
    dp[0] = Some(String::from(""));
    for i in 0..n {
        if dp[i] == None {
            continue;
        }
        for &a in &am {
            let num = match_nums[a];
            if i + num <= n {
                let dpi = dp[i].clone();
                let dpinum = dp[i+num].clone();
                let a = a.to_string();
                let right = if let Some(r) = dpi {
                    format!("{}{}", r, a)
                } else {
                    a
                };
                dp[i + num] = Some(max_answer(dpinum, Some(right)));
            }
        }
    }
    println!("{}", dp[n].clone().unwrap());
}

type Answer = Option<String>;

fn max_answer(left: Answer, right: Answer) -> String {
    match (left, right) {
        (None, None) => unimplemented!(),
        (None, Some(r)) => r,
        (Some(l), None) => l,
        (Some(ref l), Some(ref r)) if l.len() < r.len() => r.to_string(),
        (Some(ref l), Some(ref r)) if l.len() > r.len() => l.to_string(),
        (Some(ref l), Some(ref r)) if l < r => r.to_string(),
        (Some(ref l), Some(_)) => l.to_string(),
    }
}