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)

#[allow(unused_macros)]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

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

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

#[allow(unused_macros)]
macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

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

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

    ($next:expr, bytes) => {
        read_value!($next, String).into_bytes()
    };

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

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

use std::cmp::max;

const TBL: &'static [i64] = &[0, 2, 5, 5, 4, 5, 6, 3, 7, 6];

fn main() {
    input! {
        mut n: i64,
        m: usize,
        mut a: [usize; m],
    }
    a.sort();

    let minu = a.iter().map(|&a| TBL[a]).min().unwrap();
    let maxa = *a.iter().filter(|&&a| TBL[a] == minu).max().unwrap();

    let mut ans: Vec<usize> = vec![];
    while n / minu > 18 {
        ans.push(maxa);
        n -= minu;
    }

    let mut tbl = vec![None; n as usize + 1];
    let mut rest = solve(n as usize, &a, &mut tbl).unwrap();

    while rest > 0 {
        ans.push(rest as usize % 10);
        rest /= 10;
    }

    ans.sort();
    ans.reverse();

    for v in ans {
        print!("{}", v);
    }
    println!();
}

fn solve(n: usize, a: &[usize], tbl: &mut [Option<Option<i64>>]) -> Option<i64> {
    if n == 0 {
        return Some(0);
    }
    if let Some(ret) = tbl[n] {
        return ret;
    }

    let mut ret = None;
    for &c in a.iter() {
        if TBL[c] <= n as i64 {
            if let Some(rmax) = solve(n - TBL[c] as usize, a, tbl) {
                let cur = rmax * 10 + c as i64;
                if ret.is_none() {
                    ret = Some(cur);
                } else if ret < Some(cur) {
                    ret = Some(cur);
                }
            }
        }
    }

    tbl[n] = Some(ret);
    ret
}