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)

use std::io::prelude::*;

fn input<T: std::str::FromStr>() -> T {
    let stdin = std::io::stdin();
    let token: String = stdin
        .lock()
        .bytes()
        .map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().unwrap()
}

#[allow(dead_code)]
fn with_stdout_lock<F: FnOnce(std::io::BufWriter<std::io::StdoutLock>)>(f: F) {
    let out = std::io::stdout();
    let w = std::io::BufWriter::new(out.lock());
    f(w);
}

#[allow(unused_macros)]
macro_rules! debug {
    ($var:expr) => {
        match &$var { v => eprintln!(concat!(stringify!($var), "={:?}"), v) }
    };
    ($var:expr, $($vars:expr),*) => {
        match &$var { v => eprint!(concat!(stringify!($var), "={:?} "), v) }
        debug!($($vars),*);
    };
}

fn main() {
    let n: usize = input();
    let m: usize = input();
    let a: Vec<usize> = (0..m).map(|_| input()).collect();
    const INF: i32 = 1001001001;

    let nums = [10, 2, 5, 5, 4, 5, 6, 3, 7, 6];
    let mut dp = vec![-INF; n + 1];
    dp[0] = 0;
    for i in 1..n + 1 {
        for &a in &a {
            if nums[a] <= i {
                dp[i] = std::cmp::max(dp[i], dp[i - nums[a]] + 1);
            }
        }
    }
    let mx = dp[n] as usize;

    let mut rem = n;
    let mut ans = vec![0; mx];
    for i in 0..mx {
        for &a in &a {
            if rem >= nums[a] && dp[rem - nums[a]] == dp[rem] - 1 {
                ans[i] = std::cmp::max(ans[i], a);
            }
        }
        rem -= nums[ans[i]];
    }
    ans.sort_by_key(|&a| -(a as i32));

    with_stdout_lock(|mut w| {
        for a in ans {
            write!(w, "{}", a).unwrap();
        }
        writeln!(w, "").unwrap();
    });
}